Not sure how many of you have Android based phones or tablets, but I've released a free Maths Puzzle game called Sky Field - play.google.com/store/apps/details

This is far from a FPS and nothing at all like Quake 3, but any math nerds may enjoy it :]

There are no ads as well, and for about $1 (US Dollar) you can unlock the Achievements and Statistics parts of the game. That is only in-app purchase, unlike a lot of "free" games.