Back in 2001 there was a startup called IonKey which used early Lucene to search over all desktop documents - emails, Word docs, PDFs, browser cache... Didn't survive harsh post-dotcom crash.

I just installed https://www.lesbonscomptes.com/recoll/ today and it's exactly that. Super extensible and super fast once you built an index.

I only had to add a global file exclusion rule .* which prevents the indexer from scanning dotfiles. (The 'interesting' dotfiles are in a repo anyway)