NesCafee tin can has prooven to be an excellent soldering surface, so I used it to build a windmill clock. The hour hand is the windmill rotor and the minutes are displayed as a street light using a 7 segment LED display. The motor that rotates the hour hand is from a disasembled old printer. This clock also includes a BLUETOOTH module for synchronizing time via Android application. That was my first Android app. This clock is for sale for a good price.
I constructed this from 2 old bicycles for my wife and I to ride together. The two chain rings are connected so that they rotate at the same time, so when one rider turns the pedals, the other must do so too. The rear chain rings are doubled, so another chain leads to the rear drive. I used a candy box for the lap and a voltage stabilizer to limit the voltage of the wheel generator to 5V, so the LED's do not burn out.
While I work by my computer, I often forget that my coffe is getting cold. I do know that there are heaters that I can by, but they work on USB and are only up to 2,5W. That keeps the coffe only mildly worm, so I built my own which uses a Tablet charger of 5V/2A. The heater is of 8W using miniature resistors (SMD) and a thermostat I built using couple of transistors. At the bottom, there is a micro key which turns the heater on when a cup is placed on it.