ArraySync is a networked QuickTime synchronizer for multi-screen presentations, offering playback of QuickTime content across multiple displays attached to one computer or over a local area network as if it were coming from a single video source.
The software is available from App Store. The server is reasonably priced, while the client software is free. All in all a compelling alternative to Dave Jones DVD synchronizers, and worth checking out next time there’s a need for synced multiscreen video.
HC Gilje also pointed me towards the free Multiscreener. From the screenshots, it seems clear that Multiscreener is made in Max. I guess that while testing the application, one should check if playback is smooth or jittery (pardon the pun).