Microsoft OneNote for PC and Mac is Free

Microsoft is distributing OneNote for Windows and Mac for $0.

The free PC version has fewer features than paid version.  Missing features include SharePoint support, Outlook integration, and version history.

Microsoft also offers an OneNote Service at OneNote.com.  OneNote Service features:

Finally, Microsoft may release Office for iPad later this month.  Office for iPad will include OneNote, in addition to Word, Excel, and PowerPoint and will likely require an Office 365 subscription.