I've added the following myself:
* mattermost
* purple-signald (waiting for https://github.com/NixOS/nixpkgs/issues/188384)
* purple-events
* purple-libnotify
and added slack from nixpkgs.
I'm also trying to make signal integration work.
Not sure whether I'll keep pidgin, as I expect video calls from within
slack not to work.
But would be cool to have a single open source messenger instead of x
instances of chromium as wrapper around closed source web applications.
Daniel Siepmann