This program transmits sound recorded from microphone to some other devices running the same program on the same network segment, so works like Walkie Talkie radio.
Devices find each other by Android NSD (aka Bonjour), no any configuration required. Unfortunately Android NSD implementation is not stable enough, so sometimes application can not establish connection properly. Application restart or device reboot usually helps. Audio data is being transmitted by the unicast channel (TCP/IP), so each device works as a server and as a client at the same time.
Program was implemented as a demonstration of JS-Collider: Java high performance scalable NIO framework, see https://github.com/js-labs/js-collider.