Besides MUDs, TinTin++ also works well with MUSH, Rogue, BBS, and Linux servers.
The Windows port named WinTin++ (using the PuTTY derived mintty 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.
TinTin++, aka tt++, is a free MUD client for Mac OS X, Linux, and Windows.