DOS is your Operating System. You can use Windows 3.11, GeoWorks, or DeskMate as your Application Launcher.

On Android systems, a launcher is the home screen plus a little more. iPhone doesn’t have this concept as there's only one "launcher": the home screen. On android, however, you can install apps to radically change your home screen layout. Some are terminals, some are just A-Z lists of your apps, etc. A launcher on Android TV would be more significant because it would probably include movies, shows, and music instead of just apps.

It's just like a Chromecast (HDMI dongle), but running Android TV.

The closest comparable thing may be Nvidia's Shield.

If you search for "popular launchers" you should be able to find some examples

“Launcher” is the Android term for a graphical shell, the thing from which you launch apps.