Any discussion of "state machines" is not complete without a mention of Statecharts (or Harel Statecharts) [1] [2] [3]. The hierarchy and triggered actions are a really excellent way of representing a state machine.

[1] https://en.wikipedia.org/wiki/State_diagram#Harel_statechart

[2] https://statecharts.dev/

[3] https://www.wisdom.weizmann.ac.il/~harel/papers/Statecharts....