Beginning with the earliest MUDs (Multi User Dungeons), on through today's MUSHes, MUXes, MOOs, MUCKs and all the other varied offspring of the original MUD, there have been text-based multiuser games around since the early days of the Internet. But to connect to these MU*s, you generally need a client slightly more advanced than plain old telnet!
Atlantis is a client specifically designed to aid in playing those type of games. It is designed from the ground up entirely in Cocoa, and integrates with system services ó such as the Mac OS X spellchecker ó as much as possible.
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.