A system has a primary unit (1) and a number of secondary units (16), which may be stored in receiving slots in the primary cleaning unit (1) or be coupled to the primary unit. The primary and secondary units are configured as movable cleaning or grounds maintenance units capable of performing at least one cleaning or grounds maintenance operation. The primary unit (1) is powered by a power source (2), which also powers the secondary unit (16) or charges a power source (17) in the secondary unit (16). Each unit has a communications module (13, 25) capable of communicating with each other and/or a remote location. At least one of the units (1, 16) may include one or more proximity or near-field sensors and/or one or more sensor for sensing the performance of the unit (1, 16).