I'm sure you guys have all seen block exchangers before, they use pistons to switch between 2-4 different blocks. This is a machine that allows you to switch between 9 different blocks, and with lots of patience it could be extended higher, but be warned, for every row of new blocks to be exchanged, the complexity increases exponentially. I'd suggest not trying to go above a 12 block exchanger unless you have lots of redstone experience incredibly high patience. To change blocks, press reset, wait for pistons to stop firing, then push the button on the right-side wall that corresponds to the block you want. I have it set up with Glowstone, Netherrack, Netherbrick, Stone Brick, Cracked Stone Brick, Mossy Stone Brick, Iron, Gold, and Diamond, but switching out the options is as simple as pressing reset, finding the block you want to replace (only from the left, right, or top side. The blocks on the bottom are aesthetic and don't move), and switching it out with the new block. Don't press the button to switch blocks before resetting the machine, or it'll usually break.