What is "greenfoot"

Greenfoot is an interactive Java development environment designed primarily for educational purposes at the high school and undergraduate level. It allows easy development of two-dimensional graphical applications, such as simulations and interactive games.

Greenfoot is being developed and maintained at the University of Kent, with support from Oracle. It is free software, released under the GPL license. Greenfoot is available for Windows, OS X, Linux, Solaris, and any recent JVM.