DevClient is a highly customizable MUD client designed to be friendly and easy to use. It features full parsing of ANSI color codes, support for aliases, macro binding, keypad navigation, MCCP 1 and 2, accounts and automatic login management, prompt parsing, logging, and more. Its functionality and graphics can be extended with simple server definition files. It can be easily translated into any language. It can detect when a new version of itself is available and upgrade itself without restarting.
Zombie Nation MUD (ZNMud) is a Multi-User Dungeon engine. It is based on the Teensey engine for its lower level socket handling. It was designed to play out zombie outbreak ideas but can easily be expanded to host other concepts. It's a massive multi-player text-based game (although it does support MXP). It also supports modern day weapons, etc.
The Second Life Viewer is the client for logging into the Second Life 3-D virtual world, where residents explore, purchase virtual land, open businesses, build real estate, and create scripted objects such as cars, robots, or magic wands. Second Life residents retain full intellectual property rights for the digital content they create and upload, including avatar characters, clothing, scripts, textures, objects, and designs.
Deliantra is a client for Deliantra game servers. It offers an intuitive user interface for exploring the vast game world, a persistent minimap, powerful macros and keymaps, dialog-based NPC interaction, and easy configuration for the skill, spell, and item system. It is based on Perl, SDL, and OpenGL for high performance on modern systems, and works on both Unix and Windows. Ports to other platforms should be very easy and are underway.