what is the major difference between Ktor and http4k.org?

http4k vs ktor http4k -> Toolkit for serving and consuming HTTP services in a functional and consistent way. ktor -> Web backend framework for Kotlin. Easy to use, fun and asynchronous. Use Ktor (http://ktor.io/) for all projects.

well, ktor is also consistent and functional

in this case, "consistent" refers to the symmetric HttpHandler interface (actually a typealias) which is used to represent both server services and HTTP clients. Because of this symmetry, you can plug one into the other, which is really powerful - for example a unit test for a server endpoint can be reused as a test to a remote server by just switching out the HttpHandler with an HTTP client.