I don’t see RxJava and Ktor as being mutually exclusive. RxJava is a tool for reactive programming and observing a stream of data. I’m less familiar with Ktor, as I’ve experimented with it lightly. From my understanding, it’s a tool for running Kotlin based web services on platforms such as Google Cloud Platform. I believe you can use RxJava within a Ktor made application if useful for your scenario.