LitterMaid LME9000 Elite Mega Advanced Automatic Self-Cleaning Litter Box
For multiple cat homes the "mega" size of the LME9000 is the perfect solution.  The unit comes with 4 waste receptacles and 4 carbon filters and an ionic air cleaner to eliminate odor.  The paw cleaning ramp reduced the amount of litter tracked outside the box.  Light sleepers will appreciate the sleep timer that can be set to prevent the unit from activating during the night.