@janvladimirmostert Coroutines in Kolin is a solution for async programming in Kotlin code. Kotlin coroutines cannot suspend execution inside Java code, but Quasar can. In this respect, coroutines both replace Quasar (if you have Kotlin-only code you might be able to use Kotlin coroutines instead) and supplement it (without Quasar you cannot suspend Java code). Coroutines and Quasar fibers aim to solve the same problem (of async programming), albeit the approach different. The answer on the question “what works best?" is very domain-specific. To figure out that answer for your particular domain, I’d suggest reading the guide: 
https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md Please join 
#C1CFAFJSK for further discussion.