Well, I haven't paid anything for the idea knot as I am a mac user, and the mac version is free. I have yet to see free mac software for writing that I really like, but I found avenir and really like it. It's created by a writer, and I don't mind forking over 20 dollars to another writer for all his work.

I don't even know if I would want to recommend software to people for writing, frankly. That's really personal. I think the only way to find writing software for yourself is to do the research and download the ones you can find for testing.