The SCHTHACK server is a reverse engineered server for Sega's Phantasy Star Online for the Dreamcast, Gamecube, and PC. It was created on December 17, 2003, by using server logs gathered from the official server before Sega shut them down.

Both versions of Phantasy Star Online for the Dreamcast are supported, as well as all both versions for Gamecube, and both versions for PC. Xbox versions are not supported, as they are connected to XBOX Live. Note that Gamecube Episode 3 is supported, however not all card functions work. Players from other console versions can talk to each other in the lobbies, but they can not play the game with each other.