Fallout Online (also known under the codename Project V13 and FOOL) is an upcoming massively multiplayer online video game (MMO) set in the Fallout universe that is being developed by Masthead Studios and being published by Interplay, with members of the Interplay team providing creative control and design. Chris Taylor and Mark O'Green, two of the creators of the original Fallout, are among the developers.

Like other MMO's, Fallout Online is likely going to have quests that are accessed from non-playable characters (NPCs). As revealed by Interplay, they have created a large and multi-part "game-worldwide meta-puzzle". This meta-puzzle includes the puzzle structure, code system, and planned locations, which is designed to foster cooperation and competition among players for an extended time period. - Wikipedia