Nibble Writer on Steam ($10) is wonderful.
You'll have to export it a certain way to make it look correct (had several tries, and the spacing looked horrible. Finally set it right.)
Since you buy it from a "gaming" store, it actually have trophies for writing. Such as 1000 words in one day, reaching 50k words for a novel, or something. For a while, it actually encouraged me to write more, and that's coming from a guy who hates to write out stories (love making it, writing takes too long).