I built a Garden Cottage for my wife and she needed a way to store the rakes, shovels and other implements inside the shop. I first made a shelve that had holes to drop the tools in. It was too difficult to remove them. I then took the concept of a gun rack and made a larger version out of particle board that was screwed into the sides of the wall studs. This concept could be fabricated out of other materials or even molded. A foot could be added to make it free standing or horizontal brackets attached to fasten it to wall studs. A simple solution to my wife's problem and it is in use currently.
I have looked for a similar products but have not found one so far. It seems too simple not to have been done by someone. I would have expected it to be at Home Depot.