Lincity: Sim City "Classic" for Linux
Update: There is also a Unix version of the game that seems to be under development that will be included with the OLPC.
Sim City is a great game. I've played the classic version on Windows 3.1 and find it to be a lot more entertaining than newer versions. When I first set out a couple of years ago to find this game for Linux, I found a great clone that seems to be little played today: Lincity. It is available in the Ubuntu repos as lincity.
Lincity has a very simple and easy interface that shouldn't take too long to figure out even if you have never played SimCity before. If you have played SimCity, then it is a no brainer.
To be more helpful, whenever you click on a new item to build for the first time, you get a friendly help file. These are often written as though the developer is leisurely explaining it to you… not in the style of most documentation. At first this seemed strange to me, but I have come to rather like the developers' style.
Sadly, Lincity hasn't been maintained for about four years. Nonetheless, I have never experienced any real issues with it in the time I have played it. I definitely recommend old Sim City fans to try it out, as well as those who have never played the original. If you are interested in a Sim City 3000 type game for Linux, then you can try Lincity-NG, which is a more recent version of Lincity.

