Ask HN: Workflow Orchestration tools?

Are there any (simple) tools out there where the API contract is like:

- POST a statechart to something to kick it off/validate transitions/log events, schedule waits/etc

- receive POSTs (webhook-like) back to a handler endpoint to actually execute side effects

The SCXML spec defines stuff that supports this really well (ie the send/invoke tags)

Closest things I’ve been able to find:

Stately/XState

Temporal

AWS Step Functions

Step functions probably the closest to what I'm looking for but is the task token thing the only way to “receive” events?