Ulysses has been a popular writing app on OS X and iPad for a while now; however, earlier this week, indie development shop The Soulmen released Ulysses for iPhone, allowing users to write on the go.
Ulysses is a Markdown text editor that works well for anything between a blog post and a novel, giving it great utility for all kinds of writers. Now, with the iPhone App, users can sync between the different devices the app supports in a streamlined process that allows writers to work on their projects anywhere.
The app allows users to write and export in different formats, and competes with apps like Editorial, 1Writer, and Scrivener. If you wish to buy it, note that you would not have to buy the app multiple times on different devices.