Having recently installed Crunchbang and written a report on bringing modern games to Linux, it was in my interest to check out a few open source games. The past few nights I have been obsessively playing Battle for Wesnoth, a turn based fantasy strategy game freely available to Windows, Mac, and Linux.
If you are enthused by Sid Meier's Civilization series, you will likely also be entertained by BfW. The map is out on a hexagonal grid, covering various types of terrain. A single unit can occupy spaces, and the battle is led by a players heroes, who can recruit units from a keep, as shown below:
The thing that has been drawing me to Wesnoth the past couple of nights are the campaigns. The sense of purpose is a great thing to have in a game. Here is the list of campaigns included in the vanilla version(at this time)
taken from the wiki
That's a lot of adventure! To me, these strings of campaign missions are more enjoyable than a civ game where you start simply with the objective to “win”. I realize that you can download player-made scenarios for Civ 5, but the fact that all of these came included was very attractive to me.