Taptalk - Personal video and photo messaging
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Snapchat - Real-time picture chatting
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS
Bolt - Bolt is an open source Content Management Tool, which strives to be as simple and straightforward as possible. It is quick to set up, easy to configure, …
GroupMe - GroupMe is a mobile group messaging app owned by Microsoft.