The awesome pixel-artist Buch has just posted some cool "space colony" type assets that stroke me as very well fitting for a game similar to Revenge of the Titans, for which the source-code was released a while ago.
See here: http://opengameart.org/content/colony-sim-assets (links to RotT in my comment on OGA).
Source-code (Java +BSD licensed): https://github.com/imaginationac/revenge-of-the-titans
It's a fun little action tower-defense game with RTS & base building elements.
Might be also a fun project for a group of community members to collaborate on.