From Open Whisper Systems, “Privacy is possible, Signal makes it easy.
“Using Signal, you can communicate instantly while avoiding SMS fees, create groups so that you can chat in real time with all your friends at once, and share media or attachments all with complete privacy. The server never has access to any of your communication and never stores any of your data.
“Say Anything. Signal uses an advanced end to end encryption protocol that provides privacy for every message every time.
“Open Source. Signal is Free and Open Source, enabling anyone to verify its security by auditing the code. Signal is the only private messenger that uses open source peer-reviewed cryptographic protocols to keep your messages safe.”