Here are some alternatives to Facebook Messenger:
- Signal: robust, privacy-focused messaging platform trusted by experts (website).
- Session: forked from Signal, the app takes a step further to remove as much identifying information as possible to preserve your anonymity (website).
- Element (formerly Riot): a reactive messaging ecosystem, for peer-to-peer communication or for teams (website).
- Rocket.Chat: open-source communications hub (website).
- Tox: an easy to use app with a strong focus on privacy (website).
- Keybase: cryptography, simplified (website). Note: the company has recently been acquired by Zoom.
- Keyoxide: Keyoxide emerges from Keybase’s good ideas (distributed proofs and PGP keys), but keeps the platform free, open and decentralized (website). The project is in early stages and for now will speak most to people already familiar with the basic concepts of private/public cryptography.
- Mattermost: group chat software (alternative to Slack). Learn more or create a team on Framateam.
- Matrix: a decentralized communication protocol for software like Element.
- XMPP/Jabber: an open protocol that differs from email and which is better suited for instant messaging.
Telegram is one of the most popular instant messaging services out there, making it an interesting choice if our friends are already on board.
However, Telegram reproduces some prohibitive characteristics, such as data centralization in the hands of a private company. Security is not great either, since conversations are not encrypted by default and when they are, Telegram uses a homebrew protocol rather than international standards (which have been developed and thoroughly tested by a global community of experts).
WhatsApp is owned by Facebook. It should therefore be avoided for the same reasons as Facebook Messenger.