www.springrts.comengine allows FPS control, quite nice graphics, the only missing part is fog of war, which is currently in development. You can go as far as making parts of mechs separate and detachable.
Edit :
I forgot to add that the engine also uses extensively LUA language which is easy to learn and use. And generally speaking, re-creating the current machines game on that engine is going to be a piece of cake, only models are needed.