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

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.

Slack - A messaging app for teams who see through the Earth!

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.

Cisco Jabber - Cisco Jabber lets you access presence, instant messaging (IM), voice, video, voice messaging, desktop sharing, and conferencing.

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 !