Yes, the OneNote is free to use. I tested the online version and logged with my Microsoft account then I had the possibility of using the entire application. There is a Windows 10 version of OneNote, but it requires a Microsoft account as well in order to use it.
If you have Windows 10, press Windows Key + Q and type OneNote, but if you prefer the online version, then visit the following link: https://www.onenote.com
