You know that field in iTunes for beats-per-minute? Ever wondered what the hell it was good for? Well, now we know. Tangerine, a scrumptious little OSX app, will analyze your entire library — mine of some 12,000 tunes took 15 hours — and plop the BPM into track metadata — another 12 or so hours. So that’s nice: more complete metadata. But Tangerine actually allows you to do something useful.
Tangerine locally logs BPM and beat intensity. You can then construct playlists by selecting a frequency and intensity range and choosing a pattern.
The playlist view is nicely done. Songs are represented by their cover art and scaled vertically to represent BPM, horizontally to represent duration. You can of course save your playlists to iTunes.
This particular fruit will set you back $25.