Greenfoot

Greenfoot is 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.