There's been changes to the original system like a new splash screen, some UI feedback from QA, etc. The plane crash disaster has been removed as a result of 9/11. What is initially released under GPL is the Linux version based on TCL/Tk, adapted for the OLPC (but not yet natively ported to the Sugar user interface and Python), which will also run on any Linux/X11 platform. The OLPC has an officially sanctioned and QA'ed version of SimCity that is actually called SimCity. EA wanted to have the right to approve and QA anything that was shipped with the trademarked name SimCity. But the GPL version will have a different name than SimCity, so people will be allowed to modify and distribute that without having EA QA and approve it. Future versions of SimCity that are included with the OLPC and called SimCity will go through EA for approval, but versions based on the open source Micropolis source code can be distributed anywhere, including the OLPC, under the name Micropolis (or any other name than SimCity).

The "MicropolisCore" project includes the latest Micropolis (SimCity) source code, cleaned up and recast into C++ classes, integrated into Python, using the wonderful SWIG interface generator tool. It also includes a Cairo based TileEngine, and a cellular automata machine CellEngine, which are independent but can be plugged together, so the tile engine can display cellular automata cells as well as SimCity tiles, or any other application's tiles.

The key thing here is to peek inside the mind of the original Maxis programmers when they built it. Remember, this was back in the day when games had to fit inside of 640k so some "creative" programming techniques were employed. SimCity has been long a model used for urban planning and while it's just a game, there are a lot of business rules, ecosystem modeling, social dependencies, and other cool stuff going on in this codebase. It may not be pretty code but it's content sure is interesting to see.