The official JC3 Multiplayer modification by the nanos Team (responsible for MP mods such as the canned GTA:MP for GTA V or Mafia 2 MP).

A sandbox game with an upcoming Multiplayer Modification by the nanos Team.

The RAGE Multiplayer modification is what you are looking for.

Sadly this game has had all of its promising multiplayer modifications terminated. It is a good game regardless and well worth the cheap sale prices you can scoop it up for every now and then.

If you enjoy causing mayhem in a huge world with thousands of players, this one is for you.