I have been prototyping a FSM over the past two days and their usefulness is amazing. FSM is just a fancy term for workflow engine but I guess it goes well beyond that. I see only one problem. The size of possible actions which in this context would be a transition matrix, gets increasingly large with each possible branch. Add to that possible crossing branches and it could soon become a nightmare. The gold at the end of the rainbow is being able to tell which state an action is in at any possible time. That is just huge. The usefulness of states is obvious (for example, SqlConnection.ConnectionState) but to create a possible set of states for any object is very complex. Asnychronous actions are another good example. The problem that I am facing is that objects that need to have their state managed are endless and how do you include those objects you know nothing about? Especially when those objects do not manage their own state. Luckily, I am just prototyping the FSM and not actually building it right now. I see no great approach.