Pick the opening. Dimensions and features follow.
Closet
Reach-in or walk-in wardrobes with hanging, drawers, and cubbies.
Media wall
TV niche, towers, and base cabinets for a living room alcove.
Pantry
Shelves, pull-outs, and an appliance garage for a kitchen niche.
Mudroom
Bench, hooks, lockers, and a drop zone by the door.
Office nook
Desk, files, and library shelves in a spare alcove.
Laundry
Washer surround, folding counter, and a tall utility cabinet.