Tor Messenger is a cross-platform chat program that aims to be secure by default and sends all of its traffic over Tor. It supports a wide variety of transport networks, including Jabber (XMPP), IRC, Google Talk, Facebook Chat, Twitter, Yahoo, and others; enables Off-the-Record (OTR) Messaging automatically; and has an easy-to-use graphical user interface localized into multiple languages.

Tor Messenger builds on the networks you are familiar with, so that you can continue communicating in a way your contacts are willing and able to do. This has traditionally been in a client-server model, meaning that your metadata (specifically the relationships between contacts) can be logged by the server. However, your route to the server will be hidden because you are communicating over Tor.

We are also excited about systems like Pond and Ricochet, which try to solve this problem, and would encourage you to look at their designs and use them too.

We considered a number of messaging clients: Pidgin, Adam Langley's xmpp-client, and Instantbird. Instantbird was the pragmatic choice -- its transport protocols are written in a memory-safe language (JavaScript); it has a graphical user interface and already supports many natural languages; and it's a XUL application, which means we can leverage both the code (Tor Launcher) and in-house expertise that the Tor Project has developed working on Tor Browser with Firefox. It also has an active and vibrant software developer community that has been very responsive and understanding of our needs. The main feature it lacked was OTR support, which we have implemented and hope to upstream to the main Instantbird repository for the benefit of all Instantbird (and Thunderbird) users.