There's a recycling plant not far from where I take the train. In their yard, they have large (5' x 3') concrete blocks that are "stackable" in that they have voids in their bottoms that fit their counterpart's ridges on the tops—just like a lego.

They stack these 4 or 5 high and create huge U-shaped corrals for various types of metals.

My town does something similar to store rock stalk for the winter—these blocks are stacked and a pre-fab roof is placed directly on top.

To my knowledge, there is no mortar or rebar of any kind, and it can be undone and reworked into another configuration with just a forklift.

These are meant to be temporary, but have been there for >8 and >5 years respectively.

Somewhat related: The famed "Jersey Divider" is cast in a similar way, albeit without any consideration for vertical stacking.