It's an app that adds a redesigned menu for the Jukebox. If you're using it in Saloon or Mini-Jukebox, it will show the same list of songs that you see when you click on the menu.

To install the latest version of SMAPI, you have to unzip the folder with the mod in it into the game's directory. You can install it with any of the three installation options for any device.

The settings in the app are optional. If you want to change the list of tracks permanently, you need to change the settings in the folder.