I made a device that generates Nanoloop sync data for two Game Boys. The thing is that the user can set the ratio of sync clock of one of the Game Boys to the other, in the following ratios:

• Two in the time of four (double speed)
• Three in the time of four (three against four cross rhythms)
• Four in the time of four (1:1; the sync is equal)
• Five in the time of four (quintuplets)
• Six in the time of four (triplets)

There are also controls for controlling the speed of sync (via a potentiometer; aka a "knob") and interrupting / stopping the sync signals for either Game Boy, so that it stops.

Of course I know that this would be easy to make in Arduino or Picaxe or using an Atmel or a PIC - but all of this would require the user to program a chip in some way. The nice thing is that this design only requires three logic chips (which I bought locally for around AU$2.50 in total), a capacitor, a resistor and a pot. No programming or "special parts" are required. A Game Boy link cable needs to be hacked up.

Read the tutorial here.