UML The Good Parts: MSD (Message Sequence Diagrams) and Statecharts (nested FSMs). These two are the only useful parts of the UML, Class Diagrams are only useful for teaching, the rest is useless garbage.

But MSD is still can only describe a very basic behavior. Its only advantage over algorithms is that it’s more visual and adds a notion of a participant/actor.

If we’re talking about notation for describing behavior, then I prefer EventStorming for big picture, and Event Modeling for SW design. BPMN is also interesting, but much more technical and opionated. IMO it’s only useful if you’re already using a BPMN-based orchestration middleware.

Real-life workflows can be very complex, async, unordered, and non-deterministic. Just look at all manual bureaucratic processes that surround our daily life.