Might be a slightly unpopular opinion, but Volumio (software for a raspberry pi to run it as a headless audio system). It’s good, it’s relatively well maintained and works. But paying 7,50 a month for this software to get multiroom audio, Tidal integration and some other stuff is ridiculously expensive. That’s nearly 90 euro a year and the only thing that is actually an addition server side is syncing settings across devices and the Tidal integration (requires license fees iirc).
And sure, I can’t buy multiroom speakers for that kind of money, but damn, is it expensive.