SyncPlayer is an unofficial client that implements the syncplay protocol. It connects to Syncplay servers to sync video playback between two or more users. Use it to watch videos with your friends online. Just add a server, pick a video and make sure your friends join the same server and room.
Please note: SyncPlayer does not stream or transmit the video data in any way whatsoever. It only synchronizes video playback between users.
Syncplay clients are also available for Windows and Linux.