Merry Christmas from FreeGamer!
Lots of great new features and especially multiplayer games should be now much easier to do with hosting improvements and a lobby for browsing available games.
Another open-source RTS engine (using Mono/C# though) has also released a new version: OpenRA. Currently it is still geared toward running an assortment of older Command & Conquer based games, so you need to own these for the data. But this release adds lua scripting for the creation of custom missions, so maybe someone will come up with a libre game to run on this engine.
Last but not least, a new version of Warzone2100 was released about a week ago. This one actually includes some higher resolution textures, which is hopefully the first step to officially integrate all the awesome new art assets from the art revolution project.
Speaking of WZ mods: There is also an interesting new tower-defense mod currently being developed.