This has a nice intro to how Statecharts work from the perspective of verifying them. Model-checking has advanced quite a bit since then. However, those works are normally tied to specific formalisms. One could probably apply some of the heuristics or backends to Statecharts, though.
For a tie-in, here’s one from 2001 on test generation from Statecharts:
Automatic, Test Generation from Statecharts Using Model Checking
A GUI tool for them, model-checking, and test generation will be the biggest bang for buck. Since the rest are less valuable, I’m just going to batch my other finds in this comment. Consider this thread a multi-submission. Talk about whatever one you want.
Formal Verification of STATEMATE-Statecharts
Curry-Howard for GUI’s: Or, User Interfaces via Linear Temporal, Classical Linear Logic (2015)
A Graphical Environment for the Specification and Verification of Reactive Systems (1999)
Got one more whose link is suddenly broken on web UI’s. I’ll do it as it’s own submission if I find it.