- It is not open source, but it is free -> Free version.
- It is cloud based (OneDrive)
- Privacy? It is not a zero-knowledge solution, so you have to trust. See privacy section below.
- Platforms: PC (Win7+, Pre-installed on Windows 10), Mac, iOS, Android, and the web
- Can be used standalone, but of course it integrates well with other 365 apps: Word, PPT, Sharepoint, Teams, Excel, etc.
- Hierarchical Structure - Notebook (file) has 1..* sections has 1..* pages has 0..* Subpages
- Can embed pictures, objects and attach files
- Real-time collaboration in shared notebooks. Can make publicly accessible via a link or limit access to specific users. You can even embed your notebook in a web page.
- Decent search features
I have been using it for about 5 years. I use it on Android and on Windows 10 as an app and in the browser (Firefox and Chrome). It automatically syncs nicely between all of my devices. It usually happens so quickly, that I often use it as a mechanism for transferring a picture to my laptop [just saying, it's that easy].
I mostly use OneNote in the browser because on my current work laptop the OneNote app is more restricted, I assume because it is Office 365 and my organization has a policy that restricts using personal accounts (OneDrive actually told me that when I tried to add my personal account).
I haven't used the collaboration feature much, but I just tested it out briefly in firefox browser and in the OneNote Win10 app. App worked beautifully. Another tester (my wife) and I were able to work remotely without a single flaw. It gladly allowed us to interweave words on the same page. The same test failed miserably when we were both using firefox, but maybe it was just a temporary glitch.
I recommend separate notebooks based on the level of privacy you want. Anything that is super private, like your life depends on it, shouldn't be stored in OneNote (Maybe LastPass).
we collect data about your usage of the service, as well as the
content you store, to provide, improve, and protect the services.
My overall interpretation is that they don't intend to use the content, but even if that interpretation is correct, you still have to worry about internal bad actors or defects misusing your data since it is not a zero-knowledge solution. So, it boils down to trust.
For more security that is still shareable, you can Password protect sections which implies zero knowledge. However, since this is not OSS we have to trust that the password is not sent to MS? Locked sections cannot be searched (makes sense) and if you forget your password your data is lost, so I recommend using LastPass.
For more security that is NOT shareable with limited accessibility from other devices, store your OneNote notebook in a Personal Vault in OneDrive. Here is a good article. Although Vault may be good for other types of files, it currently has limitations for OneNote. First, it does not show up in the OneNote applications. You have to unlock your vault and click on the file. I was only successful in opening the notebook using Chrome on Win10:
- Chrome on windows successful.
- Firefox failed.
- Android: It did not show up in my OneNote Android app. I could see the file from my OneDrive app, but it tried to open in OneNote unsuccessfully. I couldn't access it from Chrome browser either (mobile nor desktop version) from my phone.
For even more security that is not accessible by you on all of your devices, I think you can use OneNote 2016 application and store the file locally encrypted. I think this defeats the point though.
For the most security don't use OneNote, instead use a zero-knowledge, probably less-featured, solution like LastPass.
OneNote Web version docs
Comparison of web and app version by Microsoft
OneNote FAQ It appears that OneNote will continue to be free, but Office365 subscriber will start receiving premium features as of 2020.