Steam News announces a free weekend is underway for Sanctum 2 between now and 3:00 pm EDT on Sunday. The tower defense/first-person shooter hybrid is also on sale for the duration of the event for 85% off. Coffee Stain Studios also announces the release of a big new patch for the game "that fixes a lot of stuff" and also adds the Linux and OS X edition of the game to its default branch. Here's the pitch on the game:

Sanctum 2 is the sequel to the world’s first Tower Defense/FPS hybrid game. Pick from four unique character classes and embark on a mission to protect the oxygen-producing Cores from hordes of deadly aliens who are threatened by their existence. Outfit your character exactly the way you want through the new and extensive customization system. Choose your own loadout of towers, weapons and perks, but choose wisely because you are humanity’s last defense against the unrelenting hordes set out to destroy it.