Writespace converts Word into a full-screen, minimalistic editor
It's not some half-assed macro which makes the background dark and changes font color; it was developer using Windows Presentation Foundation as a Word add-in, and is available as an installer for Word 2007 and 2003.
It's comprehensive. Writespace implements its own Find and Go To dialogs, and lets you change the margins by dragging them. It also has its own status bar. You can either "enter Writespace mode" from within Word (it adds its own button to the View tab of the ribbon) or launch Word directly in Writespace mode.
Since it's a Word add-on, that opens up some very interesting possibilities. My own Word installation is heavily customized with tons of VBA macros I have written over the years, and being able to use all that power while still enjoying the illusion of minimalism can be quite nice.
Personally, I will not be switching over from WriteMonkey anytime soon. But if you really need the power of Word yet crave the minimalism of a dark, blank screen -- Writespace seems like the way to go.
I just wish the developer would release an installer for Word 2010...