In Signal you also need a phone number to use it, which means it is also not anonymous. Also, all the communication has to run via the Signal server and you can never know, which software runs on their servers. Signal is not p2p.

Briar primarily is a messenger that focuses on mesh network communication that works via WiFi and Bluetooth. It also works with TOR, but all the mesh communication adds complexity to the whole project and the more complexity there is the more attack vectors there will be. Speek only works via the TOR network and the protocol is very simple. It is basically just 2 hidden services that are communicating with each other. This simplicity has many advantages in the long run: For example, extending the protocol to also support channels (like in Telegram) is much simpler than compared to Briar. Also, Speek already supports some features that Briar does not support, like simple p2p file sharing.

XMPP is not p2p. In the XMPP protocol someone has to run the servers and you have to trust these servers. Speek on the other hand is completely serverless, the clients can directly talk to each other via TOR. The advantage is that you always control all your data and no meta-data can be stored by the server.

The big difference to Session is that Session uses the Oxen Blockchain and that messages are stored temporarily in the Swarm. This adds an attack vector to the system, because now you depend on the Oxen Blockchain. Speek! only needs the Tor network to function properly. It is important in security to minimize dependencies and to focus on simplicity. At the moment Session has some features that Speek! has not implemented yet, for example, voice messages and group chats. On the other hand Speek! supports p2p secure file sharing of arbitrary sized files. Session only supports file sharing for up to 10MB.

Yes, Speek! supports p2p anonymous file sharing.

Yes, Speek! is opensource. You can find all the code on our Github page.