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.
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.