Hot news for today! A project unknown to me so far just released its first alpha of their upcoming open-source RTS Galactic Vice. It's still at a very early phase, and they are looking for contributors, but as you can see in this video (action starts at 0:45) it's looking like a great start already:
Their aim is to create a RTS similar to Starcraft2 or Dawn of War, and they are making good progress towards this goal. Currently you can even download the alpha binaries for Linux64bit and windows 32bit.
Very interesting is also their approach to create a tile based 3D map system, for which some examples can be found here. They are also plan on using Blender3D as their content creation tool, which is cool ;) Not so cool is that only the source code is GPLv3, while the data is CC-NC-ND >:( Edit: They plan on releasing the data also somehow under the GPL... lets wait and see how exactly. Edit2: After some discussions I was able to convince them to license the data under CC-BY-SA and GPLv2(or later)... really awesome!