A freestanding portable partition panel system is provided for open office spaces and the like. Each panel includes a skeleton-like frame having two vertical uprights positioned adjacent opposite side edges thereof, and at least two pairs of horizontal stringers attached to the outer faces of the uprights in a vertically spaced apart relationship to rigidly interconnect the same. One or more horizontal rows of slots are defined in each of the stringers. Cover panels are detachably mounted thereon to provide ready access to the frame. The cover panels permit access to the slots, and special off-module connectors with hooks for engaging the slots are provided for interconnecting adjacent panels in off-module positions. The hooks of the connectors are engaged with selected slots to hold a first partition panel perpendicular to a second partition panel in an off-module position on its face.