About 20 or more years ago my parents had installed a rolling closet rack system. The system contained a square shaped metal trolley on four metal wheels that slid in to the track which was attached to a closet shelf. You can put at most three hangers per each trolley and have as many "trolleys" on the rack.
Anyone know if they manufacture this system today? Beats a rod hands down. Don't have a picture since they have moved years ago.