From the horse's mouth -- I mean, from the developer of Scrivener, Keith Blount -- this reply. He refers to three "interesting" Windows-based writing programs (apart from the standard-issue Word or OpenOffice) I've often heard mentioned too: Page Four, Liquid Story Binder, and Rough Draft:
As for Page Four, I do mention it on the [Scrivener] main page because it seems a very solid Windows writing package, although it's been a few years since I tried it. Scrivener's "snapshots" feature was inspired by the one in Page Four, in fact. Another good PC program is Liquid Story Binder - a lot of users seem to really like that. [He added compliments for Rough Draft, but noted that its creator had ceased development.]
Other reader testimony to similar effect:
I came across a program recommended to me some years ago as "the PC equivalent of Scrivener". The program is Liquid Story Binder XE, from Black Obelisk Software (http://www.blackobelisksoftware.com/). It's fairly inexpensive at $45.95, which includes free upgrades. There's a small but responsive and helpful support community, and a support wiki has just been launched.
I find the storyboarding and, for lack of a better word, repository-like features especially helpful. [Storyboard feature below; click for larger. I assume the graphic-novel background does not come standard, but who knows.]
From another reader:
If you use Firefox, there's an extension named Zotero that is PC and Mac, and does pretty much everything you were describing in Scrivener. It starts in the actual browser and moves out from there. It also can be integrated directly with Word & other leading word processors.
Zotero has always looked very impressive as an online research and data-organization tool, but I've never given it a serious try. Maybe someday soon. In the meantime, please see for yourself. I hope it turns out to be the right answer for some people who try it out.