Cheap, cordless drills are amazing tools. Take one apart and attach a speed controller, you got a motor for a robot. Also, they have good high torque motors that can be used for all sorts of things. A $50 RC transmitter and a receiver make good remote uses, such as remote detonation. More useful tools are pneumatic cannons. I've used them from pressure testing to damage testing. WHat are your useful, unconventional tools?