
We’ve mentioned Signal Messenger before in quite a few guides. Signal is a free and open source, cross-platform encrypted messaging service developed by the Signal Foundation and Signal Messenger LLC.
It uses the Internet to send one-to-one and group messages, which can include files, voice notes, images and videos. Its mobile apps can also make one-to-one voice and video calls, and the Android version can optionally function as an SMS app.

Riot.im is out of beta. Riot.im is a free, open source and decentralized chatting platform based on the Matrix protocol for real-time communication offering end-to-end encryption. It can bridge other communications via others protocols such Slack or IRC, and it’s available cross-platform ( including web browsers ). For more info check out the 