Apple is set to bring automatic app downloads to OS X 10.8 Mountain Lion when it debuts later this summer. As noticed by 9to5Mac, the latest build of OS X 10.8 Mountain Lion only has a partially working Automatic Downloads feature, but users can expect to see a finalized working version when OS X 10.8 ships.
Automatic Downloads is currently a feature of iOS which allows the same app to be downloaded instantly on all a user's devices (iPhone, iPod touch, and iPad) no matter what device the user chooses to download the app on