Threema is described as 'New mobile messaging app that puts security first. With true end-to-end encryption, you can rest assured that only you and the intended recipient can read your messages' and is a very popular instant messenger in the security & privacy category. There are more than 100 alternatives to Threema for a variety of platforms, including Android, iPhone, Windows, Mac and Linux apps. The best Threema alternative is Signal, which is both free and Open Source. Other great apps like Threema are Telegram, Element, Tox and bitchat.
An alternative Telegram client based on TDLib, with higher speed, slicker animations and experimental features.
United Arab Emirates
ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.
United States
Speek! is the first messenger that is anonymous and censorship-resistant by design. Speek! messenger encrypts all messages and is secure, private and decentralized.
A fork of Signal for Android with proprietary Google binary blobs removed. Uses OpenStreetMap for maps and a websocket server connection, instead of Google Maps and Firebase Cloud Messaging.
Estonia
EU
VeilidChat is a 1-to-1, person-to-person text only chat application which serves as a technology demonstration for the Veilid application development framework. All communication is end to end encrypted, authenticated, private routed, and peer-to-peer. It's currently in early beta.
United States
SchildiChat is a Matrix client based on Element with a more traditional instant messaging experience.
GermanyEU
Quantum-resistant encrypted messaging, video/audio calls, and file transfers in the browser with optional registration and no downloads required.
United States
Vector encompasses the ideals of freedom through free and open-source technology, using a "Privacy by Principle" approach. This means that privacy is not a feature or add-on, but the core foundation that Vector is built upon, which is granted and accessible to everyone.
Bitmessage is a P2P communications protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities.
Sphinx.chat lets you use your lightning node to talk to anyone else who is running lightning and a sphinx compatible chat client.
