Screenshot: 

The fastest and most versatile MUD client from the creator of zMUD. Runs on Windows XP SP2 and Vista.

Features:
* Compiled scripts are 2 to 10 times faster than zMUD.
* Vast majority of zMUD scripts run without any changes in CMUD.
* Compiling is performed behind the scenes. Your scripts just magically run faster.
* Scripts are saved to a new database format...no more corrupted settings!
* Scripts are automatically saved, even if your computer crashes.

Screenshot: 

What is Mudlet? It’s a free, open-source and cross-platform MUD client that works on Linux, Windows, and Mac OS! Designed to be fast, efficient, and user-friendly.

Mudlet features Lua as its scripting base and a rich client API to support it. Split screen, auto-completion from output and input, multi-session gaming, HTML and text logging, replay recording and playback are all part of the package.

Mudlet also features a rich UI api for creating your own labels and buttons anywhere on the screen and changing their looks

Special focus has also been placed on the speed of the client.

Screenshot: 

TinTin++ is a free mud client that runs on the Windows, Linux, and Mac OSX platforms. A Windows XP and Vista TinTin++ port named WinTin++ is available for those who do not use Cygwin.

Screenshot: 

WinTin .NET is a Windows port of the popular *NIX client TinTin. It requires the .NET framework 1.1.

Screenshot: 

zMUD is the fastest and most versatile MUD/Telnet client for PC/Windows, with over 50,000 registered users. This sophisticated GUI client supports multiple character windows (multiplaying), aliases, triggers with complex pattern matching including regular expressions, macro keys, variables, speedwalking, spell checking, automatic map generation, equipment database, graphical buttons, extensive built-in and user-defined functions, ANSI color, Simutronics game support, VT100 support, MSP, MXP, MCP, MCCP support, GSL, Pueblo emulation, word wrapping, alarms, and online help.