AI Plays Punch-Out!! and Loses to Glass Joe: My self learning NES AI really fights Glass Joe, the guy who has won one fight in a hundred. It knocks him down, runs out of hearts, turns pink, and loses. The trash talk is an AI voice reacting to what actually happened in the fight.
The Amiga I Built From Scratch: A brand new Amiga computer called a DeniseITX, built by hand from a bare circuit board and a parts list. One of every part, soldered under a magnifier for hundreds of hours. It worked the first time, and I still use it all the time.