Some of them will open up the musical capabilities of html5, which are pretty cool. Example, once you switch on the ‘web-audio‘ setting on Chrome, if you use a suitable musical musical library you could play a note just by issuing these javascript commands:

var n = Note.fromLatin('A4'); 

var freq = n.frequency(); // returns 440 
var name = n.latin(); // returns "A" 
var octave = n.octave(); // returns 4

The full example (with sound, if you’ve turned on the Web Audio setting as mentioned above) can be seen here: musicjs demo.

More info about web audio and related stuff can be found on this blog post: http://pixelist.info/web-audio-it-is-finally-almost-here/