The Logitech Media Server (Slimserver) is still being developed [1] and coupled with Chromecast Audios (through squeeze2cast [2]) or Picoreplayer [3] works as a great multi-room system for me. Spotify integration is available through a third-party plug-in, Spotty [4]. Someone is even developing a great Material design skin for the web interface that is mobile compatible (and works great in a Hermit web app) [5]. Control apps exist for Android and iOS (iPeng [6]).
[1] https://github.com/Logitech/slimserver [2] https://forums.slimdevices.com/showthread.php?104614-Announc... [3] https://www.picoreplayer.org/ [4] https://forums.slimdevices.com/showthread.php?111217-Announc... [5] https://github.com/CDrummond/lms-material [6] http://penguinlovesmusic.de/