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.
psyced is a distributed chat and messaging system based on the Protocol for SYnchronous Conferencing. PSYC is multicast and routed between servers and clients in a scalable and efficient way, but users can also comfortably use IRC clients, telnet, Web chat, WAP, or Jabber to enter the network. psyced also communicates with the network of Jabber/XMPP servers and hosts programmable chat rooms for all of these technologies at once. It also provides gateways to several IRC networks, but unlike IRC, everyone can run a server and be an equal member of the PSYC network. It supports PSYC, XMPP, IRC, TELNET, HTTP, Applet, SMTP, WAP, XML, RSS, and TLS.
DutchPIPE allows Web developers to make virtual multi-user "avatar" environments. Each Web page becomes an abstracted environment or location where visitors and other items on the page are visualized. This status is retained as visitors move around. A lot of real-time interaction is possible, resulting in persistent interactive page environments. DutchPIPE uses AJAX and the DOM for the browser, and it works without Java, Flash, plugins, or firewall adjustments.