Dialogflow - Conversational UX Platform. (ex API.ai)
Chadder - Encrypted messaging app
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
GrapheneOS - GrapheneOS is an open source privacy and security focused mobile OS with Android app compatibility.
Botpress - Open-source platform for developers to build high-quality digital assistants
Earlynote - A time-travelling messaging app