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.
TiddlyWiki - a non-linear personal web notebook
A5 - Takes notes in your browser. Elegant & simple.
Personaldb - Note taking with non-linear power
Knotable - Cut the noise out of busy email threads
Roam Research - A note-taking tool for networked thought