I've used the (free) https://drakonhub.com service to create Drakon diagrams, and I've been able to express some pretty sophisticated workflows in a clear, intuitive way.

One of the things I love about it is that it is orderly by design. You've probably seen those scary flowcharts where arrows are pointing willy-nilly, criss-crossing each other, and there's very little cohesion. Drakon charts help avoid that by being relatively prescriptive about _where_ diagram components are placed. For instance, the happy path should form a skewer shape.

The "Diagramming is different with DrakonHub" section of https://drakonhub.com shows you the difference well.