While the new workflow package only supports Finite State Machines, it's designed with the ability to add new semantics, such as petri nets, or something else entirely.
What's your use case? The ability to require that some action be performed by a number of people, one after the other, before we can move on to a new state?
In that case, that might be something worth grafting on to workflow itself, regardless of whether it's FSM or Petri Nets.
In any case, acs-workflow is effectively a discontinued package, so I'd recommend that you look into 'workflow' instead.