Top 5 Free open source games

The following is a list of free open surce game, you can play these games for free and, if you're so inclined, dive into the code and modify the game to suit your exacting requirements?
so out our favourite open source games and start playing !!

1. Secret Maryo Chronicles
2. UFO: Alien Invasion
3. FreeCiv
4. Alien Arena
5. The Battle for Wesnoth