Flowable is a BPNM system. You can do a lot of async calls with it. https://www.flowable.com/open-source

We use it for a complex pricing process that invokes 30-40 micro services that can take up to minutes per step.

Kamelets and the Karavan UI in combination with k8s and Knative for "serverless" integrations looks interesting.

We at magniv.io are building an alternative.

Our core is open source https://github.com/MagnivOrg/magniv-core

We can set you up with our hosted if you would like to poke around!

We are using prefect+dbt and I like it. Altought they are doing huge rewrite at the moment.