The Battle for Wesnoth was the first game I that I installed and played after getting Ubuntu. I consider it the best game available on Linux platform (maybe except Braid). Sadly I am not equipped with enough C++ or Python knowledge to contribute.
I second the recommendation. It's a great game. It may look simple, but it's quite deep and has a great storyline. It's the first game that actually forced me to start making notes. Also, starship duels in multiplayer (which consists only of starship duels) is so much joy!!.
Just because they’re looking for programmers doesn’t mean you can’t contribute! Many of the games scenarios need maintainers, and Wesnoth has a friendly and budding add-on community that is always looking for new content.