Multiple old-school radios - my easy, no-frills option for multi-room audio
I have a FM radio player in the kitchen connected to a wall power outlet. I have a portable radio (a 1991 Sony) I can carry around to any other room.
Then I play the same FM station on both. There is absolutely no delay/latency between the two. Such a simple way to have multiple-room home audio!
No pairing, no syncing. So easily scalable - just get a few more cheap radios. Anyone in any room can independently turn it off and on.