I haven't used any of these before, but the thread piqued my interest.
Some of the suggestions here have had a lot of work done to them and it shows in the attractive UI.
I wanted to try Contour (not mentioned here), but it wouldn't install - I just got a "package unzipping" message or similar, and then nothing. So far I have yWriter, Storybook, WriteWay, and StroyBox that I am having a play with.
yWriter so far has me a little more hooked than the others, because it allows me to import an image of the location I am writing about - whether it be a map, a landscape or a room. Though it doesn't allow me to edit the imported text as far as I can see, which would make it unsuitable for me.
I like those applications that allow me to write and edit within it, rather than just import "completed" prose. (From experience, I regard very little that write as "finished."
) There are limits to how strong the editing tools need to be, but as somebody who sets up his pages with paragraph styles routinely, I would probably miss this feature. And what if the importing didn't include links back to the original file?
I haven't looked at how easy or otherwise it is to get the finished text "out" of these applications - if I want to get the manuscript to a publisher, for example - but I shall at some stage.
Overall, I can see why these can be of use, but as yet none has become my preferred option, but we shall see as time passes.