A free program for Android, by NAVA Apps.

This app is a walkie talkie. You can use it as if you were using a normal walkie-talkie, but with a much higher quality of voice and video. It has 50 channels, and you can select a channel and talk on that channel with all other people who are using the same app set to the same channel.

With this app, you can all join a certain channel and talk to one another like you are using a real walkie-talkie. It also has the elements that a walkie-talkie has, including sound effects.

You can also send an invitation to people on a public server and let them join for a private conversation.