Knotable - Cut the noise out of busy email threads
Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
OneNote - Get the OneNote app for free on your tablet, phone, and computer, so you can capture your ideas and to-do lists in one place wherever you are. Or try OneNote with Office for free.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Alternote - OS X note-taking app for Evernote.
Penbook - The nicest freehand writing app ✍️