It is not as de-centralised as gnutella or FastTrack, since it uses hubs which connect a group of users. Different hubs often have special areas of interest. Often, hubs only allow users which share some set amount of bytes to login. Chatting is built into the protocol since the start, and so most hubs are actually small communities, more than just anonymous filesharing.
The original, and old, Neo-modus client are now rather outdated, but continues to be in wide use. A open-source client with the name DC++ has a much larger feature-set and is less bug-ridden. There are some interest to add things such as ratings and hashes to the dc-protocol/community, and mostly in a way that would still let the original Neo-modus client to cooperate with newer clients.
Direct connect hubs seems to be having difficulties to scale above 1000 users, probably due to the broadcast-centricity of the protocol.
wikipedia.org dumped 2003-03-17 with terodump