Openmix is a Kickstarter project. It’s a small device with three audio inputs. Plug in two smartphones, play music through each one, and use the big wheel to crossfade between the two. Plug in an optional third device to add sound effects, and of course one audio output to play your creation. With 3.5mm jacks this mixer can be used with any device and any set of speakers.
Plug, play and mix. The device is powered by your phone in the same way your headphones work, so no need for batteries, just plug and play.
Perhaps not the most advance mixer, but a fun device for a cheap cost. They should be ready by January next year. You can place your pre-order now on the Kickstarter page for $34 (around £20) to guarantee yourself an Openmix fader. Checkout the full pricing range options on the Kickstarter page.