It probably depends on whether you want to write in Word or not. I find using Devonthink for what I'd do in Scrivener's research folder works reasonably well. A tree of folders on my disk would pretty much work, too. I'd miss replicants and per-project tagging.

If I wrote in Word, I'm sure I would use DocxManager. The developer is a friendly, top-notch sort of guy, too.