[BookCat]

I find all the boxes in yWriter a bit confusing. Maybe it suits sci-fi and fantasy writers. I prefer a combination of Word's Outline function and Write or Die. For brainstorming ideas, Papel is quite useful.
I've tried StoryWeaver (you can get a free demo with limited function) and found it a bit silly. Once you've created characters you have to swap their genders and ages etc. Some of the results are interesting, others ridiculous. I've never worked through the entire program because there comes a point when you just don't need it anymore.
There are masses of legal freebies to try, also lots of demos. It really depends what function you want the software to perform.

Forgot to mention my favourite idea generator: mikkomatrix. I've customised mine, adding lots of new situations and objects. This is a small, free program.