The FOnline Engine is an online game engine, meant to support Fallout and Fallout 2 graphics as well as the other games files (.dat, .frm, ...). The development of FOnline Engine started in early 2004, developed by a Russian team, and has never been connected to any Interplay or Bethesda project. FOnline stands for Fallout Online.
The engine allows players to play together in a fallout world, travelling across the same worldmap, meeting the same NPCs, fighting creatures together and achieving quests. Each player's progress is stored in its pip-boy (The quests progress for example), gain experience and levels based on his individual actions, and so on.
At the end of August 2010, FOnline SDK has been released to public.