One option is to use WriteRoom which presents you with a blank screen with text. Which is kind of… it. Old School, blank screen with text. Oh, you can configure the colour of the text. And the background. Anyway, it keeps you focussed on the actual writing part of it.
The other option is Scrivener. Not only does it allow you to word process, but it manages your writing as a project.
Both save their documents as .rtf / .txt / .xml which means they’re open formats you will be able to use forever. Unfortunately, Scrivener is only available for the Mac…
Happy alternate writing!