Node-red? Great visual workflow system based on MQTT, but you can also program UIs in it (node-red-dashboard), cluster process stuff with plugins, and even program this stuff on mobile (https://github.com/alexisread/noreml). It can import/export json representations of the diagrams/code.

I've found mermaid (and vue-mermaid) useful for just the workflow representation as the diagrams are compact, though the lines don't curve like in other libraries