Guillaume 'Yomgui' Roguez offers Cube 2: Sauerbraten port on MorphOS.
To play, you will need the libraries PowerSDL 13+ as well as data from the original game available on the official website.
To start the game in a window on the desktop Ambient, launch options are "-t-w640-H480" (for a window of 640x480 pixels).
To start the game in full screen mode, simply remove the "-t".
Note that the server version has not been tested, the client version is a little buggy and the RPG version is more stable but has not been fully tested.
http://www.yomgui.fr/prv/rpg_client
http://www.yomgui.fr/prv/sauer_server
http://www.yomgui.fr/prv/sauer_client
Cube 2 website:
http://sauerbraten.org/