Purposive systems have multiple goals (pre-determined outcomes, over a set time period), with some shared outcome. (Ackoff 1971)
Ackoff, R.L. 1971. "Towards a System of Systems Concepts," Management Science, 17(11), USA.
This is the theorectical system science definition. Purposive systems can be used to do specific things. Such a system may have set functions or some freedom to choose how to achieve the goal. If it has memory it may develop processes describing the behaviors needed for defined goals. Most machines or software systems are purposive; as are humans performing set tasks on demand.