Windows only: Visually WriteMonkey is a dead simple text editor with a strong emphasis on distraction free writing. Under the hood it's packed with handy features to make writing easier.
WriteMonkey is a portable text editor which runs by default in full-screen mode with a simple black background and green text, like Darkroom on Windows and Writeroom on the Mac. Unlike the previous two applications, WriteMonkey has quite a lot going on behind the scenes. There is a progress bar you can toggle on and off to serve both as a simple motivator or as a word counter if you're writing towards a set amount of text. There is also a timer which can be attached to the progress bar. WriteMonkey supports bookmarks within the text and has a text repository, a permanent clipboard attached to the document you are working on which allows you to save snippets of text.
If you forget any of the multitude of features you can hit F1 to bring up a reminder menu or hit F11 to toggle out of full screen mode and access the menus in a more traditional manner. The default format for WriteMonkey is plain text, but the basic formatting and text markups can be exported to Word or HTML. WriteMonkey is freeware, Windows only and requires .NET Framework 2.0+. Write Monkey [via gHacks]