If you don't play, then you probably have no idea what BfW is.
http://www.wesnoth.org.
Battle for Wesnoth is a free, open-source turn-based strategic game set in a medieval fantasy world. There are several dozen different units to battle it out with spread across 14 races and 6 factions. You can play against other people over the internet or a network and against the AI in a single game or as part of any of dozens of user-created campaigns and scenarios.
The stable version I'm playing is (so far) flawlessly bug-free and quite polished-looking, relatively speaking. The gameplay graphics have a charmingly retro Super Nintendo-style look. It's easy to pick up but difficult to master, and the AI makes a nicely challenging opponent (haven't played online yet, I'd get eaten alive).
