Simcity is a city building simulation game developed by Electronic Arts, and Micropolis is an open source version of Simcity released under LGPv3 license.
Read this article written by the author Will Wright who developed Micropolis in 1992 when he worked in Simcity.
Micropolis is mainly written in Python/C++ at server side and Flash as the client side, it can play on any browsers.
Micropolis is on Facebook Application - http://apps.facebook.com/micropolisonline
View its source code - http://code.google.com/p/micropolis/