Nos. 1 and 2 are, respectively, “A New Search Engine” and “Replace Email.”
3. Replace Universities
People are all over this idea lately, and I think they’re onto something. I’m reluctant to suggest that an institution that’s been around for a millennium is finished just because of some mistakes they made in the last few decades, but certainly in the last few decades US universities seem to have been headed down the wrong path. One could do a lot better for a lot less money.
I don’t think universities will disappear. They won’t be replaced wholesale. They’ll just lose the de facto monopoly on certain types of learning that they once had. There will be many different ways to learn different things, and some may look quite different from universities. Y Combinator itself is arguably one of them.
Learning is such a big problem that changing the way people do it will have a wave of secondary effects. For example, the name of the university one went to is treated by a lot of people (correctly or not) as a credential in its own right. If learning breaks up into many little pieces, credentialling may separate from it. There may even need to be replacements for campus social life (and oddly enough, YC even has aspects of that).
You could replace high schools too, but there you face bureaucratic obstacles that would slow down a startup. Universities seem the place to start.