Lugaid has Stand Alone in the FG forums. An RTS game for Windows, although I'm not sure if it is open source and able to download and play it yet. He says:
RTS game inspired by defence games. Project is almost finished, it needs more maps and graphic sets, maybe some more units. At first Interface is quite cumbersome, but not after you get used to it.
I will also note that we have started making progress with Fortress, inspired by the classic DOS game Castles. We have a logo, a very early prototype, and a wiki. Yesterday I compiled this list of gameplay elements that basically describe the key concepts of the game. Somebody has started working on models for the game too.
If you are interested, check out what we are doing and throw in your own thoughts in the Fortress forum. It will be an entirely open source project. A skilled artist or two would be really helpful. :-)
Despite my involvement (at the moment it looks like I'll be the main programmer) I have resisted bringing it up here since I don't want to abuse FG as a platform for pimping my own projects. However we have reached a point where there's a bit of momentum and it would be a good opportunity for people to provide some input before project direction becomes harder to influence.
Anyway, I'm actually away right now (back Sunday) so it's a short one today... *vanishes*