Sachin Rekhi here, YC alum from 2007. Wanted to throw a plug out for our app Notejoy: https://notejoy.com

We've built Notejoy as a collaborative notes app. So it's not only great for personal notes, but also great for easily sharing notes with your team with real-time editing, @mentions, threaded comments, and more.

But also built with a lot of the productivity features you expect from a note-taking app, including Mac, Windows, iOS apps, keyboard shortcuts / markdown accelerators, syntax highlighting, clean distraction-free interface, and more.