tower of milk crates, zip-tied and strapped to the nursery wall
Here's the kids' tower of milk crates, made by Rehrig Pacific, who invented/popularized the milk crate and who also makes awesome crates and racks in other shapes. But it turns out that in order to get anything other than milk crates, or any color other than grey, requires a minimum order of 1 truckload: 2400 crates.
Fortunately, the grey turns out to be an awesome color, a dark, anthracite that I tell myself reminds me of the color of the first Audi TT, the Neiman Marcus edition.
The perforated crates work well next to the window, an effect we didn't anticipate. A solid bookcase or other furniture might have blocked too much light.
I zip-tied the crates together, about four per side, and then I clipped the sharp edges and pushed them into the spaces in between the crates, cleans them right up.
To attach it to the wall, I got heavy rubber packing straps with S-hooks, two per side. Kind of matches the commercial vibe.