http://robocode.sourceforge.net/
from the site ...
"Build the best. Destroy the rest. In Robocode, you'll program a robotic battletank in Java(tm) for a fight to the finish. The game is designed to help you learn Java, and have fun doing it... from a simple 10 line robot to a very sophisticated, intelligent robot that destroys the competition!"
My kids and I have entered robots in the Portland Robocode League. My robots are named Fortran, Algol and Pascal. -- WardCunningham
I've set up a Robocode wiki at:
Are your robots available somewhere public? I'd like to try them out against my attempt. -- PEZ
See KarelTheRobot, CoreWars