How can I open a .mmo file?

Does anyone know a good MMO?

• I am looking for a good high quality MMO. I would prefer it to be browser based but if not I would like a download that is a small file size. I would also like it to involve fighting.

• Answer:

  Team Fortress 2: a downloadable FPS game that's free to play and it is one of my favorites. It's not all about getting the most kills in death matches, but is more strategy based. There is an item mall, but you can get almost all the items just by playing the game. Players receive random items just by playing, and there is a crafting system so that you can use item doubles to create items you don't already have. Realm of the Titans: a downloadable action strategy based game. It is made by aeria games so there's more focus on the item mall but it still is a good time waster :) Runescape: I know, I know, it's over done, listed everywhere, and stupid with there members only stuff, but it is still the number one browser based MMO and there is a lot of of new stuff being added to the game all the time.