This is a mixer with three inputs and three outputs, which makes it easy to create feedback loops using guitar pedals, toys, microphones etc. In particular try making loops with distortion pedals and things like reverb, delay, flanger, phaser, or filter pedals. With some trial and error you should be able to create some sweet chaotic oscillating noisy drones. Note this mixer is passive, meaning to doesn't require any power.
Circuit: 3 x 3 passive mixer. Built by Bryan Tabuteau & Franky Yale. Designed by Nicolas Collins.