alephone.lhowon.org
Aleph One is an open source continuation of Bungie's Marathon 2 game engine, available for macOS, Windows and Linux. It supports Marathon, Marathon 2 and Marathon Infinity natively, along with third party scenarios and net maps. Up to 8 players can join multiplayer matches or co-op play, with games hosted peer-to-peer over LAN or the Internet and a global matchmaking lobby.