WhatsApp is the largest messaging platform with over 5 billion users, bought by Facebook in 2014. In 2016 Facebook in collaboration with Moxie Marlinspike’s Open Whisper Systems, upgraded WhatsApp security by the use of end-to-end encryption.
In 2018 Open Whispher Systems started Signal Messenger LLC under non profit organization called Signal Foundation.
Signal was stormed by too many users that the verification code sent to users phone during registration was delayed.
In comparison to WhatsApp, non-profit organization owned signal uses no data of users except their phone number. Signal is well-known for protecting its users privacy. So it is widely used by security experts, privacy researchers, academics, and journalists around the world.
Along with Elon Musk many have suggested the users in India to switch to other messaging app like Signal and Telegram instead of using Facebook.