Linux only: It will only ever truly support Jabber/XMPP/Google Talk, but Synapse, a new alpha-level IM app, is a pretty—and pretty efficient—way to chat if you’re all about open-source communication.
The developer of Synapse has a goal of spreading the love for XMPP, which is an open, extensible chat standard. That’s great for the open-minded set, and users of Google Talk, which conforms to the standard, but is obviously a bit restricting, given the number of contacts one might have on “legacy” systems like AIM or MSN. There might be room in the future for server-side conversion of other protocols to XMPP, but for the time being, it’s open-source or the road.
That said, even in a theoretically buggy alpha, Synapse looks great.
Synapse is an alpha-testing release for Linux systems only. Installation instructions are available for Ubuntu, openSUSE and