Red Orchestra 2 was recently furnished with the huge and free Fall 2012 Content Pack, which included the free, re-imagined Barashka map from the original Red Orchestra as well as a free, redesigned Countdown mode. So swept up in this frenzy of free were Tripwire that they've gone ahead and made Red Orchestra 2 completely free for an entire weekend. If you're on Steam you can partake in the hardcore multiplayer FPS as much as you please between now and Monday December 17.
Furthermore, if you find your complementary time with Red Orcestra 2 sufficiently enticing, Tripwire are offering 75% off purchasing the game for the whole of that free weekend. Here's the trailer celebrating the Fall content.
Autumn. Autumn Autumn. There, that's better.