For 24 hours, everyone will be able to permanently unlock a copy of Red Orchestra 2 in their Steam libraries.
Update 2: That's all folks! The game has returned to its discounted price of $9.99.
Update: The free period has officially begun, head over to the game's Steam store page to add it to your library by the end of the day!
Original Story: "Free weekends," that is, making certain games free for all players to literally "try before they buy" for a limited time are nothing really new for Steam titles (especially multiplayer ones), but, the team behind Red Orchestra 2 is doing one better, allowing users to play the game for free, and then keep it forever, provided they add it into their Steam libraries at some point during April 23 (tomorrow). This is somewhat similar to the way Valve gave away Left 4 Dead 2 last Christmas.
Immediately following this period, Rising Storm - Red Orchestra 2's expansion pack - will be getting one of the aforementioned free weekends, where it will also be available to purchase at a discount. A very crafty business move any way you look at it - give away the vanilla game for free in the hopes that people will like it enough to buy the expansion.
"If you've been trying to convince a friend to play Red Orchestra 2 with you, there will be no better time than tomorrow!" said a developer, on the game's official Steam community page.
To unlock the game, you simply need to "add" it to your library from its Steam store page during the 24 hour period - you do not have to download it or play it for it to register.
A very nice gesture from Tripwire Interactive. I played Red Orchestra 2 when it first came out, and while it was too hardcore for someone who'd grown up on Quake, I'm sure fans of more realistic military shooters would appreciate it. But hey, can't complain about a free game!