Ask HN: App for writing notes in the margins

I am looking for an app that will allow me to read books, take notes, and reference the notes at the page I took them. I would like to be able to do this from my computer or phone.

Is there an obvious app I've missed that will allow me to do this? I've tried Evernote and Mendeley previously. Both seemed to work for simple papers but were missing common book reading tools.

Thanks.