Killing Floor 2 [official site] is currently making its way through Early Access and by all accounts is a pretty good co-op zombie blaster. Developers Tripwire are now planning to add microtransactions to the game, letting players buy in-game items using real money. The initial items will be cosmetic, bought directly or by paying for keys to unlock randomly dropped item crates, though there are plans to add weapons “with new gameplay” in future. These items will be available to everyone on a server if one person has paid to unlock them.
None of this is a surprise – Killing Floor 1 had paid DLC weapons and skins – except perhaps that the microtransactions are being added here before the rest of the game is finished.