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/