https://github.com/sentriz/gonic is a very lightweight implementation of Subsonic (so you can use any Subsonic client with it, ie. there are native and browser apps). I use it with DSub on Android.
There's still https://bandcamp.com/ for buying music, but there are many artists I can no longer buy mp3's from now that Google Play Music is gone :-/
this is the most frustrating part of the whole ordeal, many indie artists had their digital albums on GPM and youtube music is not a replacement because you can't buy albums on it.
on the other hand bandcamp is awesome, I wish more artists would use it.
There's still https://bandcamp.com/ for buying music, but there are many artists I can no longer buy mp3's from now that Google Play Music is gone :-/