Backpack is hands-down the most flexible of the online organisation tools, and it just keeps evolving. It provides plenty of options, but doesn't try to railroad you down one particular way of working. If you want to use tags, that's fine. If not, that's fine too.
This wasn't the case when it originally launched – pages had specific forms, and it was necessary to use silly tricks to sort them in the sidebar – but the new version is completely open.
It's still perfectly suited to a single user, although many of the new features of late have been focused on pushing it as a tool for small groups. There's a mini Twitter-style feature for status updates and a shared calendar for organisation.
None of these bar your path if you don't want to use them, and it's very easy to just work with basic notes. Subscription options depend on how many pages you want and how many people need to use it.
The Solo plan is $7 for one user and 100 pages, going up to $99 for 40 users and 50,000 pages.