Here’s another “useless machine” variant.  The trick to this one is that it has dual “fingers” and can work either way. Which way it turns off is selectable via a switch on the side, and the fingers can both be turned on to “fight” each other. Check out the video here.

This video depicts the assembly of a Gameboy MAME-style cabinet. For those wanting to try something like this, this video may fill you in on some of the required assembly techniques, such as how to put decals on the side of your cabinet.

This video featuring the “Autonomous Ultimate Wall-E” shows this robot’s navigational skills around the house.  Additionally, it has some nicely actuated arms.

The Verbalizer is a microphone designed to be used with Google’s voice search. It’s also designed with Arduino compatibility in mind and is open-source. Could be a good tool for your next hack.

These clever multimeter probes were built using pogo pins used in electrical test equipment. The springs inside of these pins help keep them planted firmly on the test point in question and reportedly gives a very good connection.