You are downloading the Sound Stack APPX file v2015.226.1900.204 for Windows Phone. Sound Stack is a free and useful Music app: Sound Stack, a Microsoft Garage project, is a music creation app for musicians and hobbyists. Use your phone like a drumstick to hit ... You can now download the offline APPX file to install & try it.
Download Locations for Sound Stack 2015.226.1900.204 APPX file
Note: To install it manually from an SD card, you should choose one of the server location above to get the offline Sound Stack APPX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.