My field is data analytics, and the companies that come to mind are Vertica, Tokutek, Hadapt, Autonomy. Clearly Palo Alto has Cloudera, Hortonworks, Trifacta, and I'm sure countless others. I was generalizing incorrectly.
The point I was really making was that most YC startups are focused on solving for inefficiencies in various verticals (inspired by AirBnB I guess). Very few are focused on core CS. So I was pleasantly surprised to read about CoreOS.