RexPad - Nimble collaborative note-taking.
Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
Indigrid - Plain text outliner with side-by-side views.
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.
Google Drive - Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
Memo - Simple and elegant notes app on your Mac