Shairport Sync is an AirPlay audio player – it plays audio streamed from iTunes, iOS, Apple TV and macOS devices and AirPlay sources such as Quicktime Player and ForkedDaapd, among others.
Audio played by a Shairport Sync-powered device stays synchronised with the source and hence with similar devices playing the same source. In this way, synchronised multi-room audio is possible for players that support it, such as iTunes and the macOS Music app.
Shairport Sync runs on Linux, FreeBSD and OpenBSD. It does not support AirPlay video or photo streaming.