Unknown Worlds is celebrating this weekend's PAX East gathering by kicking off the first free weekend for Natural Selection 2, their action/strategy sequel. This will begin today at 1:00 pm EDT (17:00 UTC) and the game will go on sale at that time for 50% off as further temptation to purchase it for those who enjoy the free weekend. They celebrate the news with a Natural Selection 2 Free Weekend trailer showing off the game.