ARK: Survival Evolved has been gaining traction in Steam Early Access since it released in June. They've been making strides in updates, marking itself among the number of successful examples of Early Access. Celebrating their new DirectX 12 support, they've opened the game to the public for free for this weekend only (8/27-8/30).
Also thoughout this weekend, according to their Steam Announcement page, Hundreds of new servers will feature a "One-time only Extinction Event Metor Impact" and special crates that hold artifacts. Within these artifacts can be found 50% codes for the game. Playing the game this weekend for free could grant a huge discount to continue playing. Being survival of the fittest however, somebody could easily kill you in game and steal your codes.
There are also tournaments called "Unnatural Selection" where player tribes can battle others for a chance to ride a dragon. In a very Hunger Games like fashion, these tournaments drop players in the center of the map where they can either loot the cache of equipment and risk fighting over it or running away to regroup. The ultimate goal of course is to tame the dragon as their own.
These tournaments only run from 6 AM Saturday to 11 PM Monday, so those who have bought that game can participate past the free weekend. A massive 144-player championship match will take place at 2:30 PM September 1st with real cash money prizes.