DJ equipment has advanced by leaps and bounds in recent years, but digital music formats? Not so much -- unless your software is clever enough, you usually have to mix whole tracks rather than just the parts that make sense for your set. Native Instruments aims to fix that with Stems, a free and open file format tailor-made for the DJ crowd. The tracks will play as usual in most music apps, but the right software lets you independently control the bass, drums, melody and vocals. You could drop singing if you don't want it during a transition, for instance, or apply effects to the beat without touching anything else.