The source code of the classic urban-planning simulation game,
SimCity, has now been
released under the GPL. You can find it
here. The code is based on the original, UNIX/X11/Tcl/Tk version of SimCity, with a few changes: (a) the game has been renamed to Micropolis (which was its original working title), as "SimCity" is an Electronic Arts trademark for their commercial urban-simulation games, (b) it has been ported to the OLPC XO-1 (the cute green laptop being given to children in developing countries), and (c) everything has been placed in a C++ class and bound to a Python interpreter, making the entire game eminently hackable and extensible in Python. Let a million hacks bloom.