Not for query parameters sent to the remote server, but there are definitely pages/applications that store state in the hash.

For example, look at the URLs used by mega.nz, or any encrypted pastebin (they store the decryption key in the hash so it's not sent to the server).

Backbone JS uses hash for routing. Case in point - http://backbonejs.org/#Router. There should be lot of sites that uses hash params as routes which still exists from the early SPA era.

It was used in SPAs. It was a common technique in the mid-2000s up to 2010 or so.

But not for query parameters per se, for app state stored in the query string (and bookmarkable).

https://stackoverflow.com/questions/15238391/hash-params-vs-...

One that quickly comes to mind...

https://store.steampowered.com/tags/en/Adventure/#p=3&tab=To...

It is in client-side JS single-page-apps...

lots of older or poorly written SPAs use the hash exactly in this way. I guess their fault for being poorly written, like those people who allowed GET requests to /deleteaccount based on the theory that you had to be logged in with a browser for it to ever happen and not considering that google would make an extension that did all get requests on a page on entry.