I thought I& already found the best example of a BILLY hack already —these built-ins from Gwen of Makerista, which we posted early last year. Then this project came to my attention, and I& made room in my heart for two loves instead of just one.
This is such a great customizable solution to hang plant containers. The pots and their water catching drips sit inside the boxes. I've got a couple of wooden CD crates I now feel inspired to paint yellow and fill with terracotta potted plants.