So can we come up with an meaningful definition of 'cool'? There is an infinite number of arbitrary 'cool' things in the world - audio perception is definitely interesting, but so is granular synthesis, binaural audio and physical modelling.
I'm just not sure if the role of HN is to educate users on 'cool' things. Maybe its because most of the US is currently sleeping...
On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
