Very similar to Visio, you can use Dia to create a wide variety of diagrams, such as flowcharts and relationship charts. You can save your pieces to an XML format and export them to EPS or SVG formats.

http://sourceforge.net/projects/dia-installer/

Blender started life as commercial 3D drawing and animation software, but is now open source and used professionally around the world. Compared to other 3D animation programs, it is light with all the features of paid programs. Available for Window, Mac, and several versions of Linux

http://www.blender.org/

amabilis is a real time 3D modeling program, that incorporates a drag and drop approach to some items. This Windows based modeling program has been around since 2000, but is actively developed.

http://amabilis.com/

ColorPic allows you to easily select a particular color from an onscreen image. This Windows based tool is easy to use freeware.

NOTE: There is a free version, and a paid commercial version which does have additional features. Make sure you get the version that your want / need.

http://www.iconico.com/colorpic/

Easy Thumbnails is a popular Windows based application for creating thumbnails of a single image, or an entire folder. Includes several methods for re-sampling the image to create the best thumbnail possible.

NOTE: There is a free version, paid commercial software is available on the same page. Make sure you get the program you want / need.

http://www.fookes.com/ezthumbs/

Irfanview is Windows based freeware that is simple enough for beginners to edit images, but with features that advanced users need. Photoshop filters can be imported to expand the feature set. Drawing tools are also included. For those interested in animated GIFs, this program helps simplify the process.

http://www.irfanview.com/

Inkscape is an open source vector graphics program with features and capabilities similar to Adobe Illustrator and other drawing programs. Files created in this program are compatible with Illustrator, but some students have stated that colors haven’t always remained true across the platforms. Versions are available for Windows, Mac, and some versions of Linux.

http://inkscape.org/

Paint.net is NOT the paint program found on Windows computers: this is a full featured image editing program similar to Adobe Photoshop. This Windows based freeware has a look and feel similar to Photoshop and can read and write to many if not all of the same formats.

http://www.getpaint.net/

Pixie by Nattyware is a color picker designed for webmasters. This Windows based freeware will give you the hex, RGB, CMYK, HSV, and HTML codes for any color you select on your page. If you have an interest in modifying this program for your own uses, it is possible to purchase the source code but the working, compiled program is free.

http://www.nattyware.com/pixie.php

xn view is a utility for converting image formats that also has some editing capabilities. This freeware is based in part on Irfanview, but is available in versions for Windows, Mac, and some Linux versions. Commercial use requires registration, but all others can just download the version they want.

http://www.xnview.com/

GIMP (GNU Image Manipulation Program) is an open source project that brings the power of PhotoShop to the masses. It has many of the same tools (though some use different icons), read and writes many of the same file formats (including PSD), and has many free plugins available for extending and adding tools and effects. The only issue that people seem to have is that it uses several windows, instead of a single window with palettes. Available for many operating systems.

http://www.gimp.org/

Winamp is a freeware media manager to watch, listen, and manage your media. Available for Windows, Mac, and Android.

http://www.winamp.com/

An audio compressor for Windows that makes lossless copies of your audio files, and can convert them to other formats. This freeware has been around since 2000 and is going strong.

http://www.monkeysaudio.com/index.html

Levelator - If your deal with a lot of audio, this software evens out the volume between tracks, speakers, etc. One trick, but done well. The Levelator is freeware for Windows, Mac, and some versions of Linux. 

http://www.conversationsnetwork.org/levelator

Audacity the open source audio capture/editing software for almost any operating system. Record live audio, convert from analog to digital, convert from one format to another, cut, paste, mix, change the speed, pitch and more.

http://audacity.sourceforge.net/

A powerful open source video editor that has many effects built in including rotoscoping. Currently available only for Linux, a Windows version is currently bein produced. Mac users, an outdated version is available

https://kdenlive.org/

OpenShot Video Editor is a free, open-source, non-linear video editor. It can create and edit videos and movies using many popular video, audio, and image formats. Create videos for YouTube, Flickr, Vimeo, Metacafe, Xbox, and many more common formats!

https://launchpad.net/openshot

Pitivi - Packed with time-saving features such as realtime trimming previews, ripple and roll editing, grouping and snapping, realtime assets management and searching, playhead-centric zooming and editing, non-modal cutting, detachable interface components, smooth scrolling, automatic zoom adjustment, Pitivi allows you to cut with ease. Like a ninja with a vibroblade.

http://www.pitivi.org/?

Aviedmux is a free video editor that can use several file types, and save in other formats. The editing process is simplified, and a macro recorder is built-in to allow automated processes. Current versions are available for Windows, Mac, and several Linux versions. 

http://fixounet.free.fr/avidemux/

Digital Video Converter is Windows freeware to convert between common video formats.

http://www.videodvdmaker.com/products.php

VLC can play almost any media file, many streaming products, and even devices such as webcams. This open source multimedia application is available for Windows, Mac, several types of Linux, and of course the source code is available if you'd like to compile your own version.

http://www.videolan.org/vlc/

HandBrake is an open source, video transcoder for Mac, Linux, and Windows.

http://handbrake.fr/

LimeSurvey allows users to quickly create intuitive, powerful, online question-and-answer surveys that can work for tens to thousands of participants without much effort.  The survey software itself is self-guiding for the respondents who are participating.

http://www.limesurvey.org/en/

Moodle is a learning platform designed to provide educators, administrators and learners with a single robust, secure and integrated system to create personalised learning environments. You can download the software onto your own web server...

https://moodle.org/

Drupal is one of the more popular open source Content Management Systems. Thousands of add-on modules (over 16,000) allow you to create a site with the features you want. This application needs to run on a web server, along with additional services such as PHP and a database.

http://drupal.org/

Joomla! Is a top open source Content Management System used by millions of websites worldwide, with versions and support in many languages. With almost 10,000 extensions for the current version, you can probably find a free module to do what you want: commercial modules are also available. This application needs to be based on a web server, though a distribution is available to install it on almost any Windows system.

http://www.joomla.org/

Eclipse IDE is an integrated development environment (IDE) used in computer programming, and is the most widely used Java IDE. It contains a base workspace and an extensible plug-in system for customizing the environment. Eclipse is written mostly in Java and its primary use is for developing Java applications, but it may also be used to develop applications in other programming languages via plug-ins, including Ada, ABAP, C, C++, C#, Clojure, COBOL, D, Erlang, Fortran, Groovy, Haskell, JavaScript, Julia, Lasso, Lua, NATURAL, Perl, PHP, Prolog, Python, R, Ruby (includingRuby on Rails framework) Rust, Scala, and Scheme. It can also be used to develop documents with LaTeX (via a TeXlipse plug-in) and packages for the software Mathematica.

https://www.eclipse.org

BlueJ is an open source JAVA compiler designed La Trobe University (Australia) and the University of Kent (England) for use in an educational environment. It is simple to install, use, and doesn't make large demands on the system or the user having a short learning curve for usage. Available for Windows, Mac, and some versions of Linux. It is best to install the JAVA JDK prior to installing BlueJ.

http://www.bluej.org/

Notepad ++ is a source code editor for use in Windows and not a compiler. So why do I have it listed here? It can work with multiple languages, it's compact, flexible, and  when dealing with parentheses, and brackets, excels at locating the matched symbols. Lots of plugins are available and this is an active development.

http://notepad-plus-plus.org/

Alice is an introductory programming environment created by Carnegie Mellon University. Though it uses its own language structure, it is similar to JAVA, C++ and C#, but uses a drag and drop command structure, and a three dimensional environment for the code to play out. Now including characters from the SIMS. Available for Windows and Mac.

http://www.alice.org/index.php

Greenfoot is another project by La Trobe University (Australia) and the University of  Kent (England) that is similar to BlueJ, but this IDE concentrates on creating graphical output so that users can see the results of their code changes. Like BlueJ, install the JAVA JDK before installing Greenfoot. Available for Windows, Max, and some versions of Linux.

http://www.greenfoot.org/home

Netbeans is the major JAVA IDE, and also the source of the JDK required for other JAVA compilers. Originally developed by SUN Microsystems, it is currently overseen by Oracle. In addition to JAVA, environments have been added for other languages including: C/C++, Groovy, and PHP and a few others. Available for Windows, Mac, and some versions of Linux.

http://netbeans.org/

Microsoft Visual Studio is one of the major IDEs for programmers who work on Windows machines. Languages covered by Visual Studio include: C++, C#, Visual Basic, and a web Development version. This is the Express version, which is free for download, but is somewhat limited compared to the paid commercial versions available at various resellers.

https://www.visualstudio.com/vs/visual-studio-express/

FOG is a Linux-based, free and open source computer imaging solution for Windows XP, Vista and 7 that ties together a few open-source tools with a php-based web interface. FOG doesn't use any boot disks, or CDs; everything is done via TFTP and PXE. Also with fog many drivers are built into the kernel, so you don't really need to worry about drivers (unless there isn't a linux kernel driver for it). FOG also supports putting an image that came from a computer with a 80GB partition onto a machine with a 40GB hard drive as long as the data is less than 40GB.

http://www.fogproject.org/

Clonezilla is a partition and disk imaging/cloning program similar to True Image® or Norton Ghost®. It helps you to do system deployment, bare metal backup and recovery. Two types of Clonezilla are available, Clonezilla live and Clonezilla SE (server edition). Clonezilla live is suitable for single machine backup and restore. While Clonezilla SE is for massive deployment, it can clone many (40 plus!) computers simultaneously. Clonezilla saves and restores only used blocks in the harddisk. This increases the clone efficiency. With some high-end hardware in a 42-node cluster, a multicast restoring at rate 8 GB/min was reported.

http://clonezilla.org/

PC Decrapifier is Windows based freeware (for personal use) to detect and remove the ‘free’ stuff that often arrives on a new computer. What sort of free programs would someone want removed? Things like an antivirus program they don’t like, the free trial to some ISP or image editing program. Computer manufacturers often get paid to put these applications on a new system, and if you’re not going to use it, dump it and have a leaner system.

NOTE: A paid commercial version is available, which must be purchased for other than personal use. They also accept donations from individuals via a one year personal use subscription.

https://www.pcdecrapifier.com//

FileZilla is an open source project for FTP (File Transfer Protocol - transferring files between internet connected computers). Client and server versions are available, easy to use, available for many operating systems, and languages. It supports drag & drop transfers, IPv6, and large files. If you need to use an FTP, this is a easy and well featured choice. 

http://filezilla-project.org/index.php

7 Zip is an open source file compression utility for Windows & Linux that deals with the major file formats, and its own widely used format. Compress individual files or entire folders. Uncompress almost any compressed archive, and create compressed executables.

Links for unofficial versions are available for other operating systems at their site.

http://www.7-zip.org/

CCleaner is a nice utility for cleaning and checking the security of your Windows computer. It scans many area of the system checking for lost, fragmented, damaged, or potentially dangerous files. The program is free, but not open source. 

http://www.piriform.com/ccleaner

ClamWin is a slick anti-virus software that’s quite easy to manage and is unobtrusive while keep your system free of viruses. That’s pretty much all I want from a package, so why pay money for McAfee to keep bugging me all the time?

http://www.clamwin.com/

ClamAV is an open source antivirus application for finding malware, viruses and Trojans. Being open source, the code is open for examination and branching, which has resulted in versions for Windows, Mac, and some Linux versions. (The version you see may depend upon the system your using to access the site.)

http://www.clamav.net/lang/en/

AVG provides basic protection against viruses and spyware for Windows machines, and has frequent updates of the definition files which this type of software relies heavily upon for finding viruses. A paid version offers additional features. 

http://free.avg.com/us-en/free-antivirus-download

Avira Free Antivirus is a basic protection system for Windows machines. The free version provides on access scanning, removal of viruses and spyware, and blocks known harmful sites. Paid versions for the home offer additional features. 

https://www.avira.com/free

Belarc Advisor is a profiler and benchmark application for Windows systems from Win 95 onwards, and examines such things as installed software, hardware, missing MS hotfixes, anti-virus system status, and some other things. 

http://www.belarc.com/free_download.html

Avast! Offers three different antivirus programs for Windows, but only one is free for personal use. The free versions has the basics by blocking viruses & spyware, but also allows a friend of yours to connect remotely to help you out. The paid versions have many more features that you may or may not need.

NOTE: There is a free version, and a paid commercial version which does have additional features. Make sure you get the version that your want / need.

http://www.avast.com/en-us/index

Ad-Aware Antivirus for Windows has a fast antivirus engine, protects against spyware, and has a gaming mode to allow faster throughput. The paid versions have many more features that you may or may not need.

NOTE: There is a free version, and a paid commercial version which does have additional features. Make sure you get the version that your want / need.

http://www.lavasoft.com/

IPCop is an open source firewall project for the Linux community. Features are similar to most other firewall products in that it is designed to protect against viruses and spyware. (Note: last update was in 2015)

http://ipcop.sourceforge.net/

SmoothWall Express is different from the other firewalls I have listed here in that it is meant to be a standalone appliance: in other words, it will be the only program running on a computer. A firewall device is a hardware system that protects a network. In this case you would setup a computer dedicated to running this firewall, and place it between your router (at home) and the other devices on your home. This is how business do it (often in addition to running a desktop firewall).

http://www.smoothwall.org/

COMODO is a leader in internet protection. They cover the range from home users to large enterprise setups, to issuing security certificates to web domains. They have a range or free products for Windows, and some for Mac, and here is a short list/description and link to their products:

http://www.comodo.com/home/free/free-protection.php?track=2767

Internet Security – includes antivirus, firewall, malware protection, and other features

Anti Malware – Detects and removes various malware

Antivirus – detects and removes various viruses, worms, Trojans…

Firewall – protects against online attacks against your system

Secure Messaging – protection for instant messaging

BackUp – make a backup of your system. Includes limited online backup storage (additional storage available for a fee, or with paid version)

Dragon – a Chromium based browser with additional security features

Programs Manager – watches the system as programs are installed, so that they can be completely removed later

System Utilities – items such as disk optimization, registry cleaner, and more

Cleaning Essentials – locates un-trusted processes and lets you stop them

NOTE: Some, but not all of the above items have a paid, commercial version with additional features that you may or may not find useful. Make sure that you download/install the version that fits your needs.

http://www.comodo.com/

Spybot Search & Destroy is freeware for scanning, detecting, deleting, and protecting your Windows computer from spyware. A Windows 8 version is currently in beta testing, so it should be ready this fall. This software is free for the individual user, but corporate users must get a license. Beware of downloading it from sites other than safer-networking (or from a link at their site) as some rogue versions have been around in years past that contained virus.

NOTE: Commercial products are available at this site for a charge. Be sure you know what you are downloading, agreeing to, and what it may cost. 

http://www.safer-networking.org/dl/

Etcher is an open source program to create a USB or memory card that behaves like a bootable CD or DVD. Available for Linux, Windows, and Mac. 

UNetbootin lets you create a bootable USB drive for various Linux distributions. Simple, free, powerful. Available downloads for Linux, Windows, and Mac. 

Dexpot is a virtual desktop application for windows. What’s a virtual desktop? Different setups for the same user. Instead of having multiple logins on a computer for different situations (one for gaming, one for work,  etc.) you can have several open and switch from one setup to another with just a couple of clicks.

NOTE: This is freeware, but a paid version is required for commercial usage. See their site for definitions. Additional programs/downloads are available. Make sure to download what you want/need for your usage.

http://dexpot.de/index.php?id=home

Quad-Lock Unit Converter is freeware from a company the deals with insulated concrete. Sounds like an odd provider, but the application is light weight and works well. It will convert almost any unit of measure to another comparable unit in just a few clicks.

The links here take to you the application page, bypassing their home page, which is just a click away should you be interested in their product.

http://www.quadlock.com/about/unit_converter.htm

VirtualBox is a desktop virtualization software, which functions to separate your physical desktop from your desktop space and applications so you can access it from anywhere. It also makes recovery of lost files much easier since all the components are saved in a data center. VirtualBox comes with impressive processing power so your desktop isn’t slowed down.

https://www.virtualbox.org/

ReactOS is an attempt to create a fully compatible operating system for Windows programs. The goal is to look like Windows XP, act like Windows XP, and support all the same programs. Currently the program is in the alpha stage (very early testing – not recommended for the technically faint of heart).

https://www.reactos.org/

Wine (which stands for: Wine Is Not an Emulator), allows various Linux systems to run Windows applications. Though this is actually an add-on for Linux systems, it is important enough to be included in the Operating System section.

http://www.winehq.org/download

ubuntu is an actively developed Linux based operating system, with minor releases every six months, and major releases  scheduled well in advance. What makes this system different is that they have various versions: desktop, server, cloud, educational, and more, along with a click to install library of applications. There is also a commercial service related to Ubuntu (Canonical) where you can purchase full support. To make it simple to install in tandem on a Windows machine, they even have an installer that allows it to install beside Windows, through Windows.

http://www.ubuntu.com/

Free BSD is a Linux distribution aimed at security offering versions for desktop, server, and embedded systems. This system can be installed on almost any system powered by Intel, AMD, PPC, ARM, and UltraSPARC.

http://www.freebsd.org/

Debian’s version of Linux can be installed on most Intel type machines quickly and easily. Also available, is a library of over 29,000 different applications all precompiled and ready to be installed.

http://www.debian.org/

fedora is a Linux based operations system which provides the basis for others such as Red Hat (a commercial based version of fedora). fedora is one of the more innonative systems, and they adhere to open source standards in all areas of development. (All the tools they use, the site they run, etc, are all from open source.)

https://getfedora.org/

GNOME is not an operating system, nor an emulator, nor a translator like Wine: it is the desktop. GNOME fills the gap between the operating systems operation, and how you interact with the operating system. Many of the Linux versions already have GNOME, but different versions might be available here. You can also learn more about the system at their site.

http://www.gnome.org/

CentOS is a Linus distribution meant for commercial class installations: think major web servers for example. Like the other operating systems listed here, it is free, but based upon a commercial release of Linux. About the only change between CentOS and the commercial version, is the removal of the branding and artwork. (Most other free Linux systems are the basis for a commercial version.)

http://www.centos.org/