Subway is a web-based IRC client with a multi-user backend and a JavaScript-heavy UI. Frontend/backend communication is done with websockets (or best available fallback where not available). The backend supports connection persistence and optional logging when the browser disconnects.

BarnOwl is a curses-based IM client forked from the  ktools owl project. BarnOwl currently supports Zephyr, AIM, Jabber, IRC, and Twitter and aims to be easily extensible and customizable through a Perl plugin interface.

Minimal IRC client

tircd presents twitter as an irc channel. You can connect to tircd with any irc client, and twitter as if you were on irc