The four-channel controller can be deceiving - it has a mixer section, two platters, play and pause buttons - but let’s not forget that it's just a MIDI device, albeit a specifically purposed one. You can use it to control other MIDI-enabled software (such as Ableton Live) as well, and this means all sorts of fun.
Mapping can get a bit complicated here - the NI Kontrol S4 needs to have MIDI mode activated, for example, but get the set up right (check the manual for information on custom mapping) and you should be good to go.
Serato has The Bridge, which is very similar in concept, but you don't need to stick to playing clips. How about controlling a synth using deck three and a drum machine on deck four? Definitely one for the advanced category, but if you’ve made it this far, we suspect that's where you think you belong.