The Detolf display cabinets from IKEA are the go-to solution for displaying any kind of small items, such as figurines or models.

The spacing of the shelves leaves wasted space if the items are small, but the design does not allow brackets for more shelves to be added easily.

There are several solutions on the Internet for adding brackets using cable clamps but my  design (which is similar to that sold by other Internet developers) can be printed  on your own 3D printer for free.