Mac OS X only: Freeware app Tangerine analyzes the beats per minute (BPM) and beat intensity of the songs in your iTunes library, then helps you create playlists based on these attributes. That means that it can be relatively easy to create an upbeat workout/party playlist, or, alternately, a relaxing, low energy list. Tangerine is quick (it analyzes up to 3 songs per second, according to their si