Xconq is the "Penultimate Strategy Game". It's not actually a game, it's a framework for designing strategy games. xconq allows design of any sort of hex-based or square-based strategy game, and comes with all sorts of scenarios made with that engine - from clone of empire to Godzilla scenario and clone of Civilization 2.

Now, if only I'd get BattleTech for this...

http://sources.redhat.com/xconq/