1. Free and Open Source software.
2. being an outliner let you structure your notes atomically as you type them; you can tag multiple blocks at once using indentation; you can focus the view on a block and its children.
3. with page and block properties you can build a relational database.
4. you can just focus on taking notes without caring too much where to put them since you can retrieve them back with queries.
5. Support for HTML and Hiccup.