SynchStep3 does what every avid music-listener wishes their MP3 player would do - it matches the beat of your music to the pace of your walking or running.
From the demo video above, it looks like it does a damn fine job. It'll scan your library, then uses the accelerometer to work out what pace you're walking. Then, it consults a database of tempos for songs and only plays music that matches.
Of course, if you're anything like us then you'll be subconsciously matching your walking pace to the beat anyway, but somewhere in between there's got to be a sweet spot that won't mean we arrive at places hopelessly out of breath after blaring out Pendulum.
Unfortunately, SynchStep3 is only available for jailbroken iPhones on the Cydia application download interface. The website says that it might eventually become available on iTunes, but we suspect there's a thorny issue over whether an app gets access to your phone's music library.
In which case, surely an excellent solution would be some sort of Last.fm mashup? We're looking forward to hearing more from Synchstep, that's for sure.