The Personal Wiki app enables you to take notes in a structure you can create an manage freely, like a website. Using wikiwords you can create notebook with linkable pages for tracking your ideas, information, todo lists, tasks, bookmarks, projects, notes, brainstorms - in short, your life - in the most flexible way.
If you enable access to Dropbox in the app, the pages will all be synchronized to your Dropbox account. The wiki uses Markdown syntax for editing the pages and stores the pages on your SD-card.
This is a free, and ad-free app.
There is also a Windows version, see the project page http://janwillemb.github.io/Ema-Personal-Wiki/ for more information.