Is that not a fairly simple technology? You're basically measuring latencies (for which there exist very accurate solutions) and accounting for clock drift (again not difficult - USB audio did that many many years ago).

I guess you can get fancy if the devices have microphones but I still think it wouldn't be difficult. Like one man-year worth of work.

Creating a web player that syncs audio across all types of IP devices where you can play, pause, fast forward, seek within a track & more as seen in this video isn’t trivial!

https://www.youtube.com/watch?v=OJ9itwp_wYc&index=20&list=UU...

How close is that? It sounds as though there is a very slight spread, but that might be just the chosen music.