ReTux uses the SGE Game Engine:
http://stellarengine.nongnu.org
And xSGE:
http://xsge.nongnu.org
The SGE currently uses Pygame, but I'm intending to develop a new
implementation that can work with PyPy (probably PySDL2 or Pyglet-based) when
the SGE reaches version 1.0. (I intend for that to happen after reTux is
finished.)
A SGE implementation optimized with Cython is in fact another possibility
I've considered. An implementation in pure-python also has the possible
benefit of greater portability, though, so that takes priority. :)
