How and where your files are saved
Ulysses tries to be a repository for everything you ever write. Open its three-pane view and you access a library and your current folder. You can rearrange files using drag and drop, create smart folders, and Shift-click multiple items to temporarily group them in the editor. You also get cross-device iCloud sync, periodic backups and powerful export functionality. Text, HTML, ePub, PDF and DOCX are supported, along with direct publishing to Medium.
iA Writer has a new Library pane – a searchable documents list that syncs with the iOS app using iCloud (although files can alternatively be saved locally). The app exports to text, HTML, PDF and Word. Byword is similar (minus a sidebar), but adds RTF and LaTeX output, and a £3.99 publishing in-app purchase for directly posting to Medium, Tumblr, WordPress, Blogger and Evernote.
The others are simpler: WriteRoom handles PDF; Focused exports to HTML and RTF; Ommwriter will export to PDF and RTF, but only allows one open document at once.
Ulysses has seriously powerful document management and export capabilities.