I enjoy figuring out how electronics work and modifying for my own use.
Created a bunch of triggers out of real drums.
Built a 6WD rover for exploration of mines. Uses a Raspberry Pi + Camera to feed back 1080p video to a computer which has real time controls. Built with a 150' tether since Wireless doesn't work well in mines.
Built a 300+ gallon aquaponics installation, and the circuitry to monitor in real-time and make decisions based on external inputs.