shairport-sync
"AirPlay audio player. Shairport Sync adds multi-room capability with Audio Synchronisation" - https://github.com/mikebrady/shairport-sync
Example
shairport-sync in docker
This is a really easy way to get shairport-sync running on Linux. The container is 12mb.
docker run \
--rm \
--detach \
--network=host \
--device /dev/snd \
-e AIRPLAY_NAME="shairport ${HOSTNAME}" \
kevineye/shairport-sync