GMud32 is a MUD gaming client, which is used as an alternative to the standard telnet interface. It has many useful features, and is simple and easy to use. Includes multiple profile support, triggers, macros, sound pack support, etc. And yes, of course, it's totally free... Great for all those new to mudding!
Runs on Windows 95, 98, ME, NT, 2000, XP, or Vista
TinTin++, aka tt++, is a free MUD client for Mac OS X, Linux, and Windows. The Windows port named WinTin++ (using the PuTTY terminal) is available for those who do not use Cygwin (A Linux/Unix emulator for Windows) and runs on Windows Xp, Windows Vista, and Windows 7. Besides MUDs, TinTin++ also works well with MUSH, Rogue, BBS, and Linux servers.