This is just for the new Android TV devices, just like the ADT-1 and the Nexus Player, it is completely useless on other devices
Android TV requires current apps to be up to date and declare themselves compatible before they're installable from the Play store.
While actually not as streamlined or seamless as the average consumer would want for his or her TV, many apps can still operate on some stage on these gadgets if you sideload them, but they don't show up within the Leanback Launcher (the Android TV homescreen).
So for that there is this app, the Sideload Launcher. A simple app that reveals you the conventional app launcher icons that a cellphone or tablet would show you, but which are hidden on Android TV, allowing you to launch any sideloaded app!