This week Steam is giving a big push to one of the indie games in its catalog. There are two different promotions live for Altitude.

Altitude is a 2D multiplayer shoot 'em up. Players pilot airplanes and dogfight with each other in seven game modes. The modes include the soccer-like Plane Ball and more standard fare like Team Deathmatch.

This weekend, the game is free to download and play. If you think it's a keeper, you can purchase the game at 50% off until Monday.