If you haven’t used it yet, pyfrc is a python 3 library designed to make developing code for RobotPy (the Python interpreter for the FIRST Robotics Competition) easier.
As one of the new features in pyfrc v2014.2.0, there is now a robot simulator GUI built into pyfrc that features many of the available objects of WPILib (a screenshot is attached). After installing pyfrc and enabling it in your robot code, the simulator is launched via your robot.py file using the following command:
python3 robot.py sim
pyfrc is available via pypi and is easily installed via pip. It has been verified to work on Windows, Linux, and OSX. Check out the website for installation instructions. If you find any bugs, please file an issue on github!