Ema Personal Wiki is a cloud-synchronized 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.
The wiki uses Markdown syntax for editing the pages.
There is also a Windows version.
Synchronization is done using Dropbox.
The sourcecode can be found on github, see the link on the Ema Personal Wiki homepage.