Here I tried to do as little as possible to get http4s running using ZIO instead of cats-effect IO
Follow the standard http4s instructions and get the quickstart app running:
sbt -sbt-version 1.2.8 new http4s/http4s.g8 -b 0.20
You can see the result in this commit:
https://github.com/apauley/http4s-zio-quickstart/commit/f0846efcbe8c212748586de727047f00ed37d042
Instantiate the Quickstart Server with a ZIO Task instead of the default cats-effect IO:
https://github.com/apauley/http4s-zio-quickstart/commit/e678d3b829230cde9195c4447683d791b7c2373b