After a casual bit of googling I'm not sure what is the current status of GUI support in PyPy. Does tkinter work with PyPy yet (It doesn't in the version I have installed here)? Is there any other GUI that you recommend? I'm looking to make a Python-based physics simulator that should be able to show animations in some kind of GUI. I would like to have some kind of web-based format as one output of this (so that results can be shown on the web) but I'm not sure how good that would be for interactive simulation. The physics calculations require that I need to use either PyPy or Cython or something (not plain CPython) to get reasonable performance. One possibility is that I could run PyPy in a subprocess from a CPython-based GUI which I guess is not dissimilar to getting it to work in the browser except I get to write the front-end in Python. -- Oscar