It's incredible how much you can do on your smartphone these days. Take the triqtraq Jam Sequencer iPhone app for example, it lets you mix music while you're riding the subway or waiting for a friend.
A whole studio of specialized equipment has been programmed into this brilliant bit of smartphone software, allowing amateur and working DJs to mess with filter, level, pitch, decay and delay on their handsets in real-time. A library of over 350 sounds is available to users starting out, or else you can upload your own beats into the mobile app through iTunes. The triqtraq Jam Sequencer can support the storage of 32 samples and 16 patterns per session and allow you simultaneously tweak multiple tracks.