Windows users have Wordpad, though most of them don't remember to look for it. It has opened anything text-like I've pointed it at, though of course it won't render anything from markup.
I use Scrivener but it has a small number of visually stylistic nasties that get in the way of what *I* need it for sometimes. These are by way of unreconfigurable personal tastes so your mileage will certainly vary.
I also recommend the napkin-back whiteboarding tool Scapple for roughing out ideas. It *is* integrated with Scrivener and the two together are ridiculously useful. Scapple has a short'n'shallow learning curve too, because it was designed from the UI back.
As for the cost of Scrivener being a disincentive to using it, I got it for $40 and consider it money well spent. Scapple cost something like $14. If "free or nothing" is your mantra then you'll pass it by, but it will be your loss.