There are currently 6 publicly available (mud)libs for DGD:
The kernel lib is the minimal lib written by Dworkin himself that is included with DGD. It provides a foundation which gives developers a working environment around which a fully featured mudlib can be developed.
Noah Gibbs' Phantasmal mudlib
GurbaLib, written by Erlend Simonsen:
I want people to use it for whatever suits them best. I made it mostly as a learning experience, as I was fascinated by how LPC muds work. If it can help anyone get started coding, set up a test mud, or start fiddling around, I'm happy. All I ask, is that if anyone finds bugs, they report them to me, or even better send me fixes.
The current release of Melville is 0.9.1 which was written for DGD 1.2. The mudlib is designed to provide all the facilities necessary for a group of developers to connect to an environment in which communication and security features exist and begin designing and writing game specific features (which have been left out to allow for such customization). This mudlib was written by Stephen Schmidt (a.k.a Mobydick).
LPMOO is quite a different mudlib in that it completely masks LPC from users and developers and instead simulates the LambdaMOO driver complete with its MOO language. It was originally written for DGD 1.0.9 by Robert Leslie. A patch is available to update the lib for DGD 1.1.
The venerable 2.4.5 mudlib was originally written for the 2.4.5 LPC driver. Unfortunately its LPC is quite dated both in design and implementation. It appears to be the only choice available, however, for people who wish to open a playable mud straight away.