While working on the FIRST Robotics Competition, I discovered team 302's VIRSYS (VIrtual Robot SYStem) project, a robot simulator and practice field. At the time it was only programmable in LabVIEW, which is a popular language in the FIRST competition, but not one that my team uses frequently. I developed an extension to their project that allows users to program their robots in Python, and later, Java.
GitHub projects: