State machines (that contain both labeled and unlabeled transition systems) may indeed serve as operational semantics of some formalisms, but they can be denotational semantics of others, or even studied completely separately from any programming formalism.
Not only process algebras, but even the lambda calculus is naturally expressed as a state machine, where the states represent the expression, and transitions represent possible reductions (lambda calculus is nondeterministic).
Not only process algebras, but even the lambda calculus is naturally expressed as a state machine, where the states represent the expression, and transitions represent possible reductions (lambda calculus is nondeterministic).