Hello, everyone. I have been playing around on cubehamster's Minecraft server, and through another member's challenge, I developed the world's smallest single-block floor door. It works as a toggle switch, so you don't need to fiddle with a T Flip-Flop. Weighing in a 4x2x3, or 24 cubic meters, there really is no way to downsize it without changing the basic mechanics or input mechanism.

http://www.mineimg.com/images/2012/12/08/6jfqA.png
(Built in Royal Purple for its world record)

Showcase:
http://www.youtube.com/watch?v=K9mWVLa9 ... e=g-crec-u