Mine is the computer. I continue to be amazed at what we can do with them.
It is crazy that. For time immemorial we used to transmit information from our mouths or using hand signals, and receive that information through eyes and ears, all in realtime.
(side thought: how awesome would it be if we had a single organ for both? e.g. communication solely through blinking)
Then suddenly we have this system where someone can code meaning onto a sheet, and we can receive entire contexts from a glance alone, purely at our leisure. Nuts.