You can download this great looking game called Energy Tycoon, for Windows and Linux, and the source-code is available under a MIT/BSD like license. It includes some non-free parts however (e.g. irrklang AFAIK) and the media license is unclear, but it's rare that such a polished game shows up as open-source more or less out of nowhere.
Quick selection of other news
A rather interesting GPL licensed racing project was recently released for the Blender game engine (BGE): SAAB-91 Virtual Race. Interesting especially because it seems to have some sort of official support by the designers of the car, but currently it is still at a very early stage.
It's also nice to see the official page of ZeroBallistics online again, even though it still needs an update. In the message-boards there is finally an official word of the FOSS release, however. Oh and I am fully aware that I am repeating myself, but this great project is still looking for additional developers!
The also previously featured Wolf:ET Xreal port is making some great progress, with the renderer almost completely ported. Oh and their website also got a nice overhaul, reflecting Xreal's new focus as a game engine rather than a game project. In related news there is a very young project based on Xreal aiming to create an open Enemy Territory, conveniently called OpenTerritory.
Last but not least there are a bunch of updates on the open-source (but with non-free media) cartoon FPS World of Padman, which them preparing for a big version 1.5 release.