Tails

Torchat is small and only has a few dependencies. It is in Debian: https://packages.qa.debian.org/t/torchat.html

More about it here: https://github.com/prof7bit/TorChat

• dedicated Tor instance

torchat in Debian runs its own Tor instance.

Quoting its maintainer in Debian: "For torchat to use system’s tor, it will have to have write permissions on the system’s Tor data directory. Which I particularly didn’t like, in comparison to use its own tor instance. This is because it needs to store/read keys for the hiddenservice to work."

Answer to that:

TorChat does not need read/write access to the hidden service folder, this is only one of the many possible configurations, it only needs to know the .onion hostname of the service. TorChat can be configured to run with an existing global Tor proxy, then you have to tell it (torchat.ini) the address and port of the socks proxy and the name of the hidden service that will receive the incoming connections. Tor must run with a hidden service that redirects to localhost:11009 and you need to make a small start script that puts the .onion name into the torchat.ini after tor has successfully started. Alternatively you can patch torchat so that it will read the hostname file on its own (make a symlink to the hostname file that it may read on application start)