There is a free, web-based version of OneNote at http://www.onenote.com/
There's a free app for Windows (Metro and Desktop), Android, Mac, and iOS that will give you access to your OneNote Notebooks just about anywhere. The features do vary a little (can input handwriting and drawing in Metro, but not work offline - Android can work offline, but no drawing/handwriting), but various articles have featured team members talking about how they plan to improve feature parity.
At this point if you really want to use OneNote you can use it just about anywhere.