Pi MusicBox is described as 'With Pi MusicBox, you can create a cheap (Sonos-like) standalone streaming music player for Spotify, Google Music, SoundCloud, Webradio, Podcasts and other music from the cloud' and is an app in the Audio & Music category. There are three alternatives to Pi MusicBox for a variety of platforms, including Linux, Self-Hosted solutions, SparkyLinux, UDOO and Raspberry Pi. The best alternative is Volumio, which is both free and Open Source. Other great apps like Pi MusicBox are RuneAudio (Free, Open Source) and Balena Sound (Free, Open Source).
Volumio is a free and Open Source Linux Distribution, designed and fine-tuned exclusively for music playback. It runs on a variety of devices, typically small and cheap computers like the Raspberry PI, but also on low power PCs, notebooks or thin clients.