A mere 19 years after its release, the original Sim City source code is now completely free. And not just money-free, but proper free, the code released under the GNU General Product License.
In order to keep EA happy, the game's name has been completely changed throughout, instead calling it by its working title, Micropolis. Apparently the ancient code has been tidied up for those wishing to mod and manipulate, and rather peculiarly, the plane crash disaster has been removed because of 9/11. (I'm fairly certain plane crashes were horrific before 9/11 as well, so I'm not quite sure why this was necessary. Earthquakes haven't exactly proven themselves to be a party-time-fun of late, but they seem to survive the censorship. But nevermind.)
The motivation for getting the code was driven by the wonderful One Laptop Per Child project, which you can find out more about here.