A two thousand kilometer diameter Diskworld in distant orbit around a Jovian class world
A diskworld is a class of ring-shaped habitat that encloses nearly its entire diameter to provide an extensive and diverse habitable volume. Aside from an open cylindrical space at the center of the disk for docking spacecraft, virtually the entire volume of the ring is enclosed and used for habitation or related purposes. Within those parameters, a tremendous amount of diversity is possible, including:
Multiple levels of habitation extending inward from the outer rim. The exact number of levels can vary widely, depending on the distance between each level. On the larger habitats, planetary scale or greater-than-planetary scale living areas are possible.
A single large habitable volume extending from the outer rim to the inner core with occasional bracing structures running from edge to edge. Airwalls and other environmental systems work to maintain an even level of air pressure throughout the structure, which supports a large aerial and arboreal ecosystem and is often home to flying or gliding sophont populations.
All or part of the disk is given over to computronium, usually supporting large sophtware based populations.
A fractal honeycomb of chambers, varying in size from meters to hundreds of kilometers across. Individual chambers or groups of chambers are designed to serve whatever purpose is desired, from manufacturing, to urban centers, to nature reserves.
Some combination of all of the above options and more. For example, a diskworld may have several levels of "conventional" habitation rings along its outermost rim with three to six large "spokes" of multi-use chamber space extending partway to the hub, which then in turn give over to large computronium banks. Between the spokes are large open volumes supporting aerial/arboreal ecologies.
In the Current Era the diskworld habitat continues to evolve. In the Orion Federation, a new class of diskworlds uses open volume designs filled with angelnet effectors and movable partitions to allow the inhabitants to rearrange their entire world in an almost infinite number of variations.
The Zoeific Biopolity has recently announced that it intends to begin construction of a new habitat layer in the Ocean's Unlimited dyson complex consisting of water-filled diskworlds optimized for deep abyssal environments (and presumably inhabitants). The Solar Dominion has announced plans to construct a mobile diskworld fitted with reactionless drives and hosting an expedition to the galactic core.