Google doesn’t not indexes, just web pages and documents, but also file types like executables, databases and source code. To search for a file with a specific extension, you need to use the operator filetype. The under is only a small reference gist, there are many more to try at Google.
1. Find applications.
If you search for [winamp filetype:exe], the first result is a direct link to Winamp 5.08. Searching for [python filetype:msi] brings many direct links to Python 2.4 setup. It’s interesting to see that Google actually indexes the files and gets some metadata from them.