Particle Director is a tool for specifying custom particle velocities for particle systems. You are able to specify motion of the particles by placing control vectors, solids, sources, sinks, etc. Velocities are then computed for the entire velocity field by running a fluid solver for a certain amount of iterations using your inputs as boundary conditions. The custom particle system fully integrates with the built-in particle emitter, animator and renderer components.
More information can be found here.
