Acheron is an upcoming modification for Battlefield 2142. It aims to offer the players the ultimate Colonial Marines experience (within the limits of the Refractor engine).
There are still things to be fixed but it's almost completed now thanks to our master Pe†eR-KuN! :))
Hm... Is it BF2142 or BF2?
It's BF2. Most things are tested in BF2 before being moved to 2142, it's much easier and faster that way. ^^