This is a selected list of multiplayer online games which are free to play in some form without ever requiring a subscription or other payment. Some common types are first-person shooters or vehicle simulation games, but could be of any genre.
List of free multiplayer online games Wikipedia
These MOGs run on a non-profit basis, requiring no payment from the players.
These MOGs run on a for-profit basis, but require no money from the player for an in-game advantage over other players.