ProtoMUCK - NeonMUCK derivative including GlowMUCK enhancements. Not much documentation. On going project. - http://protomuck.sourceforge.net/
Nameless MUCK - Commands and changes in the Nameless modification to Fuzzball. - http://nmc.limitless.org/
Fuzzball Software - The release site for classic Fuzzball 5 and Fuzzball 6. Includes documentation, third-party support, and a starting database. - http://www.belfry.com/fuzzball/