The Tor team has been working on this product for quite some time now, with three alpha versions distributed for internal testing via the project's mailing lists. Today marks the first beta version for Tor Messenger.
Tor's IM client wasn't created from scratch but coded on top of Mozilla's Instabird IM chat client. Pidgin was the other candidate the Tor team considered.
The team eventually went with Instabird because it was built on XUL (XML User Interface Language), a technology the Tor team had experience with. XUL is also a technology deployed with Firefox, the browser upon which the Tor Browser was built.
Tor Messenger comes with versions for Windows, Mac, and Linux users.
The client currently supports OTR (Off-the-Record) messages, a multilingual interface, and transport networks like Jabber (XMPP), IRC, Google Talk, Facebook Chat, Twitter, and Yahoo!.
Despite working via Tor, which allows the exchange of messages via anonymous Internet relays, masking the location of the people involved in the chat, there are some downsides as well.
The biggest of them is the classic client-server communications model that allows Tor Messenger servers to store chat metadata. The Tor team recommends that server admins implement solutions like Pond or Ricochet to counter this issue and remain truly anonymous.
The Tor team's plans for future Tor Messenger versions include support for automatic updates, sandboxing (for increased security), better support for Tor's protocols, OTR for Twitter DMs, secure multi-party communication (np1sec), and encrypted file transfers.
Below is a quick screenshot tour, courtesy of Softpedia's Mac department.