Palm OS had a system-wide search that would call each program's main function with an argument to do a search (typed in a text field in a search dialog). The call to main was on the stack of the search system without even fully launching each application. Each program could display the results that it chose based on its own search.
(Mykland, Robert. Palm OS ...
Windows NT since at least Windows 2000 has had search system built in that includes a plugin system so new types of documents can be indexed.
It was not on by default and has an interface the looked like a web search results but it worked.