Particle Flow is a versatile, powerful particle system for 3ds Max. It employs an event-driven model, using a special dialog called Particle View. In Particle View, you combine individual operators that describe particle properties such as shape, speed, direction, and rotation over a period of time into groups called events. Each operator provides a set of parameters, many of which you can animate to change particle behavior during the event. As the event transpires, Particle Flow continually evaluates each operator in the list and updates the particle system accordingly.
To achieve more substantial changes in particle properties and behavior, you can create a flow. The flow sends particles from event to event using tests, which let you wire events together in series. A test can check, for example, whether a particle has passed a certain age, how fast it's moving, or whether it has collided with a deflector. Particles that pass the test move on to the next event, while those that don't meet the test criteria remain in the current event, possibly to undergo other tests.