I really like hanging around behind grocery stores, drugstores, seeing what they are throwing out (or very carelessly storing ... I'm not sure which it is sometimes) and I always see these wire shelf pieces that wouldn't normally work without their proprietary system in the store, and wonder how they can be hacked, also I needed some shelves to hang in my sunny windows for all my seedlings and figured the shelves would block the least amount of light.
I could see these being useful out in the garden, camping, anywhere you cant drill into a wall but the ceiling would be OK, great for inside closets too.
Step 1: Get Yer Shelves
Try going behind walgreens and target and such, keep an eye out and you'll see em. I like to affect a casual "mmm hm hmmmm oh look shelves in the trash? I guess I'll just take these . . . " attitude, you dont want to get caught looking like you know are doing something wrong just in case someone has a problem with you taking them (in all likely-hood I don't really think the store wanted these since some were bent, or they think no-one will take them because they wouldn't be useful w/out the proprietary supports) I feel this is a gray area to worth investigation. I might not investigate this at a smaller family establishment, or at least then I would ask first.