There are tons of note taking / writing / outlining apps. Most have support for syncing with cloud storage (DropBox being a leading candidate). A couple of choices to get you started: Evernote is popular, online and the free version is functional. Outline is a more sophisticated app - and since you mention hierarchies, you might like this app. It's also available for Mac and compatible with Microsoft OneNote (and MS has their own OneNote app too).
Probably best to just look right here.
There is also a Mac version. You can either create it in their proprietary format or in OneNote format. It can edit and use existing OneNote files.
Another HUGE vote for WebDav support!
I currently use Outline (http://outline.ws/) which is Mac / iOS and supports WebDAV so I can use it via Owncloud or FreeNAS. But, no web interface or other OSes which is limiting.
Thanks for the reply. I actually only tried Outline because it was released before Microsoft put out their own version. It feels much more like a native Mac app than Microsoft's does. It's just hard to find so many of the editing options. I don't use many, but I couldn't even find a way to strikeout text. It don't know if it's possible or not, but I sure couldn't find it.
Also, I have tried the online version, but felt it kind of lacking. It tedious to navigate between notebooks. I also try to avoid using online apps when I can, otherwise I end up with several open tabs of distractions. I guess this is where we continue to hope Microsoft optimizes their app for Mac. It looks like Outline does have a trial version, if you are ever curious about trying it though.
The supposed fix didn't work for me either. 100% cpu usage, 100 points of battery drain.
I find Evernote unusable due to lack of zoom. Besides that, the interface is terrible IMO.
Before you switch to Evernote, maybe you should try Outline 3.0 ("best companion to Onenote"). You can download a trial version and read about it here: http://outline.ws/mac
Personally I hadn't tried it yet, but the interface seems really well designed. I'm trying several note apps for Mac and almost all of them are ugly, cluttered and outdated.
If you have the time, I'd like to know your opinion on this app.