dfasyn is a tool for constructing state machines.  The input language allows a
lot of generality.  For example, it allows repeated elements to be specified
where the items have constraints between the end of one and the start of the
next.   (I could not find a way to define such an automaton in the lex/flex
input language, which prompted the writing of the tool.)  Currently, you must
do a fair amount of work yourself to build a parser around the resulting state
machine.