Abstract: The invention is a modular frame system that can be used to construct free-standing enclosures for equipment. The modular system includes interchangeable frame members connected to transition members that can together be arranged to form an orthogonal frame. Other accessory components can be attached to build an enclosure system. The invention envisions utilizing composite materials in constructing enclosures, with such embodiments having an enhanced strength to weight ratio. The frame system is constructed of frame members that facilitate alignment and attachment of other system accessory components through use of regularly spaced upstanding male connectors that engage with regularly spaced depressed female connectors. Thus, there is great flexibility in attachment of components and adapting the enclosure system to particular applications. Frame members of the invention can alternatively be used as construction components in a variety of building systems.