Check out RoboEmu2:
http://www.robbayer.com/re2.shtml
It will require that you compile your source code using GCC, but if you can get it all working, it's a great solution!
With lots of hacking, it allows you to use autonomous mode, disabled mode and user mode and, with even more hacking, can simulate pots, encoders and even a camera as it runs through native code.
Of course, it won't probably simulate wierd problems like state variables randomly getting set to 0 by interrupts or other such nastiness. (I had this last Friday, and had to tear out the entire autonomous code between matches.) Small things like code loops or what happens if somebody has a certain switch on as it enters auton mode can be tested, and this program has helped me fix some obscure bugs in the code.
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-Patrick Horn,
Paly Robotics
Check out the space simulator called
Vega Strike, modelled after the space simulator games Elite and Wing Commander. It's Open Source too!
If you have ever played
Wing Commander, or especially
Privateer, and had a feeling of nostalga derived from the you will enjoy these two Vega Strike mods:
Privateer Gemini Gold and
Privateer Remake!
I'm working on adding multiplayer support this year...