For those who are itching to play an MMO on Linux but don't want to pay a subscription, Albion Online just opened up the flood gates.
Unlike a lot of MMOs Albion Online doesn't have traditional classes, quests and it's very much a sandbox do whatever you want experience. It's a little odd and focused a lot on player versus player combat, although the recent Oberon update made improvements for PvE and there's a lot of features for bigger groups of players and Guilds.
As a reminder, they don't seem to be doing this due to a low player-base. In fact, when they talked about the free to play release recently they actually showed the game to be growing. Even before the most recent patch, you can clearly see a slow build up of daily online users:
Worth noting that while it's free, there's still a premium subscription option which basically speeds up your progress in the game. This can be paid with real money or in-game money too which is quite nice but without it the game is pretty slow going.
If the game becomes ridiculously busy, they will have a queue system with premium users given "preferential access".