From LilyPond Wiki

[edit] LilyPads

LilyPads are communities of people interested in any sort of topics related to LilyPond. They may communicate on LilyPond Wiki, elsewise in Cyberspace, Meatspace, Outerspace, ...

[edit] LilyPads on LilyPond Wiki

• Professional Toads: a community on LilyPond Wiki interested in professional use of LilyPond.

[edit] LilyPads Elsewise

• Lilymusic: "Beautiful LilyPond scores under free licenses"
• Mutopia: "Free sheet music for everyone"
• ChoralWiki: "Free Choral Sheet Music"

(This is still a STUB. Please add some pointers to communities that you know.)