wxMUD is a GPL'ed MUD client written with the wxWidgets (formerly known as wxWindows) GUI library to support many platforms (win32, Mac, POSIX, etc) with native speed.
Currently it supports ANSI colours, multiple
connections, MCCP, MXP, MSP, and
more.
We want to fully support the MXP specification on platforms other than win32, as that's sorely lacking, but also on Windows. Also competition is good and makes things only better, so zMUD and others, watch out :-)
There have been questions about the health of the project, so let me assure you that the project is not dead, but has been on a temporary stand-still due to everyone that has contributed to the project been busy in real life as of late. The project manager is around to accept patches and contributions and answer any questions that come up. The plan for the project manager is to allocate a weekend for wxMUD work soon and push an official release out, and time-allowing getting back to the development of the project from thereon. Meanwhile feel free to join our IRC channel, which is located on the irc.freenode.net network as #wxMUD or e-mail the project maintainer (leio AT users DOT sourceforge DOT net).