This is a shelf I built using Kee Klamps and 1-3/8″ top rail fence post.
I purchased the Kee Klamps from Simplified Building Concepts, you can also get them from Grainger and McMaster-CARR prices are about the same anywhere you go (read: expensive) but Simplified Building seemed to have a better selection. The Kee Klamps are awesome and I could come up with a ton of things to build with them, but there a bit cost prohibitive to build with. All in all though they work quite well. I couldn’t find the weight bearing specifications of the Kee Klamps but I was able to stand on the middle shelf (~160lbs) without failure. This was an expensive project mostly due to the use of the Kee Klamps, but they sure are cool.