I was introduced to these lightweight, stacking supports at the College of the Redwoods. Making them is an excellent exercise in mortise-&-tenon joinery, with the added benefit that it results in a sturdy pair of supports ready to go to work in your shop. Materials are provided and partially prepared. To see some images from a previous M&T class, see this post in the blog.
Three-day workshop, 9:00a-5:00p daily
Materials: $ 50