An infinite box of cards
Doug Miller discusses, "what is Tinderbox?"
...an infinite box of index cards, which you can attach to an infinite wall. Now, in addition to those index cards and that wall, you have a very smart, very programmable, very fast robot. That robot can nearly instantly retrieve, sort, rearrange, and even change the content of those index cards at your merest whim. Better yet, it can memorize your commands and re-execute them on demand.