For the Developing of Mobile Applications Course at the University, I had to develop a WhatsApp Clone called ThatsApp. It is written in Kotlin and to that Time with Jetpack Compose in its Beta Release.
The App needed to fulfill several Requirements like having a Profile, taking and sending Pictures, sharing the users current Location. It hat to be compatibel with the App of some others Attendees of the course so we had to implement a standard API, which we self decided on, and for sendingg and receiving Messages we had to use a dedicated MQTT Channel per Chat.
https://github.com/emoba-fhnw/thatsapp-fs21-lichtwellenreiter