Micropolis

In January 2008, the SimCity source code was released as free software under the GPL-3.0-or-later license, renamed Micropolis (the game's original working title) for trademark reasons, and developed by Don Hopkins. Since Micropolis is licensed under the GPL-3.0-or-later, users can do anything they want with it that conforms with said license; the only restriction is that they cannot call it "SimCity" (along with a few other limitations to protect EA's trademarks).