Mentioned elsewhere, Everything search by voidtools: https://www.voidtools.com. It does funky things with monitoring some component of the NTFS filesystem to maintain a up-to-date index of every filename on your computer, and makes them searchable literally as fast as you can type.

(https://news.ycombinator.com/item?id=33321000)

There seems to be two kind of searching people do. Some people want a search tool that searches in documents. Some people want a search tool that searches filenames.

Everything search is exclusively the second. I think I can count on one hand the number of times I've wanted to search inside documents in the last 10+ years (and for those cases, grep has worked fine, even on windows!).

For some reason, searching inside documents seems to be the default for both windows and os x search, and it's super annoying.