Valve has plans to release Left 4 Dead 2 to gamers on the Linux platform next week, where it's slated to be tested by the developers. The developers at Valve are counting on fans of the game to aid in the development process by launching it as a public beta on Linux for anyone who already owns the game.
In addition to the Linux version, Valve is testing the game's so-called Extended Mutation System, a new feature which allows players to essentially modify the heck out of their games. Valve hopes that the new feature will bring many players back to the title, which has been out since 2010.
The Extended Mutation System, or EMS, is designed to let modders create deeper, more customizable maps and Mutations to alter the way the game is played in its entirety.
Players who want to participate in the beta—either on Linux, Mac or PC—can download the beta build, which will appear as a separate download from the main game in the Steam library of anyone who owns Left 4 Dead 2. Valve states that players participating in the beta version of the game will connect to other beta testers on servers designated for beta testing.
Source: L4D Official Blog