Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
Unit Notes for iOS - A simple and powerful note-taking app.
Draw.Chat - Anonymous real-time whiteboard with text and video chat.
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.