Google Desktop Search (it is dead now anyway). Was brilliant while it lasted.
There were some other alternatives as well but I think GDS starved them to death before Google got bored and killed GDS. (Please le me know if there are good alternatives, free/paid/open source, everything is interesting as long as they fo the same things GDS did and can convince me that they don't upload my data.)
I personally use an app called Everything[1] since I moved to win10. Win10's search indexing seems to be trash and its tendency to prioritize web results over desktop results is infuriating. Everything is good for finding something tucked away on your hard drive(s), is dead simple to use (give it a few minutes the first time around to index everything, then just search). I wish I could replace the existing Cortana with it or something else rather than opening a different app, but alas When in Windows, do as Microsoft demands.
It's amusing how simple Everything is: it just searches the file database in Windows by name. It doesn't search file contents. I am not sure why this isn't the way Windows search works.
X1 is pretty great https://www.x1.com/
No affiliation but I run this on several big workstations and it “just works” , it’s not free but I like that it works locally and doesn’t seem to choke with tons of files (and maybe 40GB of emails)
There were some other alternatives as well but I think GDS starved them to death before Google got bored and killed GDS. (Please le me know if there are good alternatives, free/paid/open source, everything is interesting as long as they fo the same things GDS did and can convince me that they don't upload my data.)