Valve has rolled out the second wave of games on Steam for Mac today, and they include the first cross-platform multiplayer games. Killing Floor, Altitude, and Madballs in Babo: Invasion now all allow for some PC vs Mac action. Said games also come with a hefty discount; Killing Floor is 33 percent off, the other two 50.
Altitude is also getting a free weekend, which is already underway.
Other newcomers for the week include (all Steam Play titles) Europa Universalis 3, Hearts of Iron 3, Sam & Max Season 2, Sam & Max Season 3 – Ep. 2, Chains, Simplz Zoo, Caster, Eschalon Book 1, and Windosill.