the cool part of battle for wesnoth with my current limited knowledge of it is it seems to be a rare example of an open source game that isn't just a version of a commercial game.
I'm slightly concerned if I learn a little more about it I'll come to find that it is just an open source remake of a commercial game.
on the plus side if it is then there's still also cataclysm: dark days ahead that I'm pretty sure is an original work.
