Signal

Signal is a free messaging app for texts, voice notes, calls, video calls and groups, like WhatsApp, but designed around privacy above everything else. Every message and call is end-to-end encrypted, always, with no setting to turn on. Its code is open source, so outside experts can check what it does.

It is run by the Signal Foundation, a nonprofit created in 2018 with an initial donation of roughly 50 million dollars from Brian Acton, a co-founder of WhatsApp. The app itself grew out of earlier apps made by the cryptographer Moxie Marlinspike and his project Open Whisper Systems. There are no ads and no investors expecting a profit; it is funded by donations.

Signal's most important contribution may be the Signal protocol, the encryption design behind it, which is considered a gold standard and is also used by WhatsApp and other apps. What sets the Signal app apart is how little it collects. Beyond the encryption, it is built to store as little metadata as possible: it does not keep your contact list, your groups or who talks to whom. When authorities have demanded user data, the company says it could hand over little more than when an account was created and when it last connected.