Besides Kotlin on Spring(Boot) and Kotlin or Ktor, is there other places we see Kotlin used with a traditional web framework? (I find http4k a little too low level to count as a web framework)

micronaut

I'd rephrase the question - what "java" web frameworks aren't being used with Kotlin. I suspect that the amount of teams using http4s, zio, ring or finagle with Kotlin is fairly minimal 🙃

They all work though. Some of them probably lack the kotlin extension functions to make using them less tedious. You can always fix that yourself of course. All the big ones seem to have those out of the box though,

but is http4k really more low level than ktor?

Maybe a little bit 🤷 . Http4k works by composing http functions from the inside-out until you get a server. Ktor is more like declaring an application, and then adding your routes and extra config to it; outside-in.

Ratpack is also kind of low level but is also there...

Thanks!