The XMPP support in Pidgin is extremely dated. There is a patched Pidgin source tree maintained at https://github.com/CkNoSFeRaTU/pidgin - you'll need to compile this for XEP-313 support. There is no plugin version.
https://github.com/dylex/slack-libpurple works nicely. To obtain a token, follow https://github.com/yuya373/emacs-slack#how-to-get-token
### Signal
https://github.com/hoehermann/libpurple-signald is built on top of https://gitlab.com/signald/signald/ - signald is needed in the background. So far everything worked, including New type groups, apart from anything SMS/MMS based; only in-Signal features/messages work.
Note: start signald system-wide, but allow the plugin to show the QR code for linking, don't try to register the account in advance, by hand.
https://github.com/hoehermann/purple-gowhatsapp is a new plugin that, unlike other Pidgin WhatsApp plugins, connects to the web interface of WhatsApp, so the possibility if immediately getting block is reduced.
### Telegram
https://github.com/majn/telegram-purple
### Matrix
https://github.com/matrix-org/purple-matrix/
Basic features only.
### Skype (web)
https://github.com/EionRobb/Skype4pidgin
Via the web interface. Might break soon due to the coming redesign (again....) of skype.
### Discord
https://github.com/EionRobb/purple-discord
### Pushbullet
https://github.com/EionRobb/pidgin-pushbullet
### Mattermost
https://github.com/EionRobb/purple-mattermost
### Instagram
https://github.com/EionRobb/purple-instagram
Makes an actual login on login - notification noise might hapen -, and it is a bit messy on contact list terms, but seems to be working.
### Facebook
https://github.com/dequis/purple-facebook/
You'll need to compile it for normal Facebook, no special tricks.
./autogen.sh # you'll probably need to install additional packages...
sudo make install
2. Restart pidgin
3. Accounts → Manage Accounts → Add
* Protocol: Facebook
* Username: your email address
* Password: wharrgarbl (it doesn't matter)
* Remember password: yes
* Advanced → Login as a Workplace account: yes
* Save, Ok
In case you get [SSL/TLS errors on connect](https://github.com/dequis/purple-facebook/issues/408#issuecomment-374275285):
- Try Tools → Plugins → NSS Preferences → Maximum Version → TLS 1.2
- restart Pidgin
If that doesn't work, and you're on Linux, you can try recompile Pidgin without GnuTLS. If you do so, I suggest using https://github.com/CkNoSFeRaTU/pidgin - this is a Pidgin patched with XEP-0313, should that be ever needed - it's useful.