VHDL/Verilog as well, but that's completely obvious.
I've been using state machines for Javascript UI elements.. really simplifies things.
Gesture detection/interaction here. All state machines all the time.
Life cycle management, process synchronization, lockfree data structure, user-space networking... I can't remember the last time I didn't use a state machine.
As someone who troubleshot networking issues for years, god bless you.