The classic urban planning simulator SimCity’s sources have been released under the Gnu Public License. Apart from a few modifications such as changing its title to Micropolis and removing the Airplane Crash disaster (9/11), the game is the same. You can dig in its code and roll out your own version of the ‘80 gaming classic or you can peek under the hood to see how games were made back then.
Either way, this is a nice gift to the community, albeit perhaps a little late.