signal
Posted on 03 November 2015
From: Open Whisper SystemsSignal uses your existing number, doesn't require a password, and leverages privacy-preserving contact discovery to immediately display which of your contacts are reachable with Signal. Under the hood, it uses ZRTP, a well-tested protocol for secure voice communication.
Signal was designed specifically for mobile devices, using a jitter buffer tuned to the characteristics of mobile networks, and using push notifications to preserve battery life while still remaining responsive. Signal is also Free and Open Source Software, allowing anyone to audit the code for correctness or help contribute improvements.
