Minecraft, Roblox, Second Life (probably, not sure whether this counts as game). Pretty much every Multiplayer Sandbox-World nowadays is able to scale up to MMO. At usually out of the box they are not RPG, even though they can be modded to be RPG. Similar things happening at GTA5 or RDR2, where the basegame is not RPG on a technical, but RPG by world-setting and gaming-style.
Then we have the endless amounts of wargames[1], shoots[2] and old browser-games[3]. Or the newer genre of battle royale, where we have hundreds of players per session in some game. Though, there is not much richful interaction between the players outside the game, it's all just simple chat or even none at all. Though, I heard Fortnite has gained some persistent world-aspects outside the game-sessions?
Other than Second Life, those aren't really persistent virtual worlds. Video game worlds, sure, but do you really see Facebook creating video games for it's blue site and instagram audience?
The oldest public minecraft-server will hit its 11th birthday next month. Not sure how much more persistence you can demand? Some of the other games also have persistence in various ways available. But that's the point, persistence is not a hard demand of MMO, it's just a strong trait for RPG. For MMOs in other genres it makes not much sense to let the player wait in some virtual graphical lobby, when a textual lobby is good enough. For an MMO, a game must support a huge number of players in the game itself, not in the pauses between the games. The definition today has become more flexible than 20 years ago.
> but do you really see Facebook creating video games for it's blue site and instagram audience?
I think their point is more that they will offer the graphical virtual space for the players to wait and meet between the games and work, while others will create the games and apps which people than can enter from this space. My understanding is, they offer technology and the connecting point, not the content. The same way they already do it today with plain old 2D crud-interfaces.
