Here's an interesting Danish Modern take on modular adjustable storage furniture. This system was designed in the 1960s by furniture designer Henning Kjærnulf. It features a variety of drawer and cabinet units, along with shelves, and is user-configurable.

The crutch-like verticals make extremely economical use of materials. Narrow as those pieces are, they're made of oak, which is strong enough to bear the weight of the components.

And as you can see, there are no horizontals in the structure; that is to say, the components themselves are the horizontals.

The system is infinitely extendable.

As for how the components are attached to the verticals, you can figure it out by studying the two photos below. The components have metal brackets on them that are shaped like an inverted U. These brackets hang on steel rods inserted into holes in the verticals. I imagine that the holes are a lot deeper than required to just hold the rod, meaning you can slide the rod deeper into a hole to free the rod at the other end. (If this is not the case, then reconfiguring the piece would require disassembling the verticals altogether.)

With this alternate design below, the holes run left-right rather than front-back. The components presumably rest on brackets that plug into holes. Sadly I couldn't find any revealing shots.

I was not able to learn what the name of this furniture system is. If any of you know, do drop a line in the comments.