GNOME Shell Extensions - Здесь нет.
Есть возможность установить какой нибудь клиент типа:

Apps/Empathy – GNOME Wiki Archive

GitHub - aluxian/Messenger-for-Desktop: This is not an official Facebook product, and is not affiliated with, or sponsored or endorsed by, Facebook.

This is not an official Facebook product, and is not affiliated with, or sponsored or endorsed by, Facebook. - aluxian/Messenger-for-Desktop

github.com


GitHub - telegramdesktop/tdesktop: Telegram Desktop messaging app

Telegram Desktop messaging app. Contribute to telegramdesktop/tdesktop development by creating an account on GitHub.

github.com


GitHub - majn/telegram-purple: Adds support for Telegram to Pidgin, Adium, Finch and other Libpurple based messengers.

Adds support for Telegram to Pidgin, Adium, Finch and other Libpurple based messengers. - majn/telegram-purple

github.com


Corebird

Turpial: Best bonus casino widgets python dev online

Turpial is a lightweight and beautiful microblogging client written in Python.

turpial.org.ve


Thunderbird — Призван делать работу с почтой легче. openmailbox.org