Multi Theft Auto (MTA) is an open-source software project that adds full on-line gaming support to Rockstar North's Grand Theft Auto: San Andreas PC game, in which this functionality is not originally found. It is the first open-source modification that adds a highly customizable network play element to a commercial closed-source single-player PC game. Developed as an experimental piece of software for earlier Grand Theft Auto series, Multi Theft Auto has become an advanced multiplayer platform for gamers and developers. Our software provides on-line gaming for dozens of players running user-generated gameplay content and scripts through a Lua virtual machine, and is freely distributed under the GPLv3 license.
It's the best multiplayer experience for GTA San Andreas for many years now and it's still in high development. You can play it for years, and it never gets old. You can't compare it to other multiplayer games out there, because it is not one "game". Actually it's a huge platform for many kinds of games. There are popular game modes I've never seen anywhere else. So for me, it is the best multiplayer game I've ever played so far.