Manuskript is an open-source tool for writers, with outliner, character management, plot development, distraction-free editor, etc.
Writemonkey is a Windows zenware writing application with an extremely stripped down user interface, leaving you alone with your thoughts and your words.
Liquid Story Binder XE is a uniquely designed word processor for professional and aspiring authors, poets, and novelists. Writing software for those who require the editing ability of a commercial text editor as well as a document tracking system.Discontinued
Last update was around 2011, can still be bought.
JDarkRoom is a popular, simple full-screen text file editor with none of the usual bells and whistles that might distract you from the job in hand. If you are writing a speech, novel, essay, thesis or just need to be able to concentrate on your writing, then JDarkRoom may help...Discontinued
Last version dates from 2010.
For Mac users to write without distractions. WriteRoom is a full screen writing environment. Unlike the cluttered word processors you're used to, WriteRoom lets you focus on writing. Requires Mac OS X 10.7+Discontinued
The program is no longer available for iOS. The Mac version, v3.2.1, released in August 2012, can be still bought from the AppStore.
PyRoom is a free editor that stays out your way - and keeps other things out of your way, too. As a fullscreen editor without buttons, widgets, formatting options, menus and with only the minimum of required dialog windows, it doesn't have any distractions and lets you focus...
The last entry on the dev blog dates from 2010.