This is an app that lets you open .docset packages (Xcode documentation sets) from the Finder. Doing so will launch Docset Opener, which will then open the docset's navigation page in your favorite web browser.
The utility of this is debatable when you can just use Dash to search installed docsets directly, but it beats Xcode 4.2's behavior, which is to open a window containing its .docset icon.