From Cerulean Studios:
Trillian for Web allows you to easily chat on your favorite IM networks without having to install any software. Trillian for web supports Windows Live, Yahoo, MySpaceIM, AIM, Google, ICQ and Jabber. Trillian is also available for download on Windows.
Version 2.0 features Facebook chat, avatars within the contact list, sound preferences, contact list views, contact list management, status messages shown in message windows and the contact list, enhanced connection manager settings, URL previews, language packs, and inline registration of new Astra Accounts.