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.

Zello - Zello's push-to-talk app redefines the walkie talkie. It's a great push-to-talk over cellular (PoC) alternative for businesses and organizations. Learn more about the best walkie talkie app in the market.

Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.

Hibox - Hibox is a mobile app that primarily functions as a platform for collaboration between team members. The software helps maintain communication while a team works on a project, and it provides privacy while supporting the pipeline.

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.

Walkie-Talkie.io - This completely free walkie-talkie app online allows you to communicate quickly and easily with your friends. Go to the same radio frequency, push to talk and that's it! There is also a mobile iOS version and always 100% free !