Single Action- The project will do any next action handling. This is for a project when the tasks are not related to each other. The project is made up of "one off" tasks.
Parallel- The project can have multiple tasks marked as next action working in "parallel".
Sequential- The project can have one next action task and when that task is completed another task in the project can be designated as the next action result in a "sequential" handling of the next actions.