Introducing Bark! Low-latency multi-receiver live-sync lossless audio streaming for local networks. It's like Sonos, but open source, so nobody can brick your devices remotely. It's also written in Rust :)

https://github.com/haileys/bark

It sends 48khz uncompressed float32 data over UDP multicast. It can achieve playback sync to within hundreds of microseconds in ideal conditions, and usually to within a millisecond.

Support for Win XP, Win 7, 3D acceleration

SoftXpand (Requires service pack 1)
ASTER

Support for Win XP only, 3D acceleration

Friendly Seats (Win 7 software in development)

hamachi alternative

HomePlug 1.0 and AV are the two versions of the specification for home networking technology that connects devices to each other through the power lines in a home

Gamer's Internet Tunnel (GIT) is a free utility to link LANs together over the Internet for network gameplay.

often is the default IP address of a (domestic) router