I've been interested in graphical formal specifications since I first heard about Petri Nets like a decade ago. It always felt like engineers would be more likely to utilize formal methods if there was a graphical representation instead of a bunch of scary math notation and language associated with it. Sadly, every time I've tried showing Petri Nets to other engineers, they get pretty disinterested almost immediately.

Before I abandoned my PhD at University of York, I was working with something called "RoboChart" and RoboSim [1], which I actually think might be more approachable, but it's pretty tied into the robotics semantics. A pet project I've been working on has been trying to adapt and extend RoboSim to something a bit more useful for the network and server world.

[1] https://robostar.cs.york.ac.uk/robotool/