I know some people have posted their MMOs or talked about them in other boards, but there is only one MMO I play- Glitch. It's MMO Cooperative world building.
Unfortunately, it's not the most welcoming to newcomers (not by fault of the community- being cooperative rather than competitive leads to an incredibly friendly user base) but because it can take weeks to learn the skills necessary to plant trees, make farms (as in, farms with crops, not gold or EXP farming), or build buildings and furniture.
It's free. The only way to pay for anything in game is clothing and cosmetic items (such as being able to reskin a piece of furniture or building you made, although a god number of the reskins cost nothing). You can't spend money to learn skills faster or get any in-game skills or items, only cosmetically modify existing ones.
I'm Xalia on there if any of you happen to play. It's still in beta, so if you want to try it out, PM me with an email you use and I can send an invite.
Also, one of the creators is the guy from Katamari Damacy, so expect weird gorgeous graphics. ESPECIALLY the quest where you learn Firefly Whistling. Man that was trippy.
Here's the actual site, in case you're interested.