If I were writing a workflow system in a hurry I'd use arangodb in the back end and a web server based on asyncio. I like the idea of something RDF-based but I'd need to develop the right algebra for isolating individual "records" in an RDF database so they can be updated safely.

I worked at a startup that built a system with quite a few parts including a system for annotating text to train an extraction pipeline. That last bit had a typescript/react front end, a scala web server, and kept data in an elaborate set of tables in postgres. They were in a hurry to get it working for one particular customer so it wound up pretty half-baked.

I have a lot of ideas on this so look up my profile and send me an email!