From Cube Wiki
The top place to look for published mods is, of course, on Quadropolis. Use either the table or the list of available mods. Always remember -- the source is zlib license, the artwork under varying (but generally more restrictive) licenses.
- Read the license, this means every available one and check they allow you to do what you want to do. In very short: you can use the source; but any media is not distributable. Their license is soley for dot3labs to distribute with Sauerbraten (except where EXPLICITLY STATED OTHERWISE -- such as free for all non-commercial use; if there is no explicitly stated license, it is for the Sauerbraten distribution ONLY). Any derived work of yours will have to either be a "total conversion" (e.g. make models and maps from scratch with your own texture set and all) or be a "Client/Server mod" (e.g. small changes to either side of the game).
- You should NEVER, ever, ever, ever run these modifications on the regular network; best approach is to edit the designated ports for your mod right away and never try to register modded servers on the Sauerbraten masterserver!
- Read the todo list and all developer info you find lying around, it helps!
- Keep a list of your changes; this is incredibly important and helpful.
- Abide by the ZLIB license.
- Take screenshots of your mod periodically and compare them to the ones on the main page . Does the mod look better or worse? Don't delete these, they'll look great as thumbnails on your "changelog" page.
Top 3 DON'Ts
- Don't copy content (textures, maps, models, etc.) without consent by the respective copyright holder (see appropriate readme's). Inquire on forum if in doubt.
- Don't use the official network/port/masterserver for your mod. This means you need your own masterserver and should use different UDP ports than the regular game.
- Don't forget open-source is free as in free speech, not as in free beer.