Knotable - Cut the noise out of busy email threads
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.
Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
A5 - Takes notes in your browser. Elegant & simple.
Notational Velocity - Notational Velocity: modeless, mouseless Mac OS X note-taking application
Alternote - OS X note-taking app for Evernote.