RexPad - Nimble collaborative note-taking.
Knotable - Cut the noise out of busy email threads
Indigrid - Plain text outliner with side-by-side views.
Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
Etherpad - Etherpad is a highly customizable Open Source online editor providing collaborative editing in...
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.