From University of Kent:
An integrated development environment that makes it easy to write games and simulations in the Java Programming Language. It comes with a broad range of demo scenarios and documentation that gets newcomers started very quickly. Greenfoot may be used to learn or teach programming, or just to put a cool game up on a website. (Yes, Greenfoot can export the game to a web page!) Originally developed for school age learners, but now used by all age groups.