Microphone Cast is a free Android app developed by Tirro Labs that allows you to connect your phone's microphone to a Chromecast or Google Home. The app uses your WiFi connection to send audio and supports both the built-in microphone for low latency voice and streaming high-quality audio using a headphone jack or USB device for higher latency.

This app has several potential uses, such as streaming music or audio from another device connected with a headphone jack or USB device. It can also be used to send voice messages or call someone in another room, set up a live microphone and speaker system, or monitor live audio from another room.

Overall, Microphone Cast is a simple, easy-to-use app that can be a useful tool for anyone who needs to connect their phone's microphone to a Chromecast or Google Home.