In automata theory, we find many applications. They are used in text processing, compilers and hardware design.

CFG is used in programming languages and artificial intelligence.

Cellular automa is used in the field of biology e.g. mollusk and pine cones.

PDA can be used in language accept or. We say that string is accepted by machine only if string takes machine to an accept state.

TM can reverse any string that has combination of any 3 variables. It finds application in algorithm, information theory, complexity studies, etc.