We are seriously impressed by this coaster idea, which looks like a ton of fun to make as well as use (we love the clicking sound of buttons against a tabletop). Contrasting thread and a pile of uniform buttons complete the project.
has the complete tutorial here
, but it's pretty self-explanatory when you look at it. We'd love to see a version with buttons of varying size and color, though that might be harder to thread into a grid.