WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...
Zulip - Chat for distributed teams. Zulip combines the immediacy of real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.
React Native - A framework for building native apps with React