This is a special order fallboard lock. I can't say it's the best one on the market as it tends to fall off at times.... and it's moody.... and makes noise. Nonetheless, it's low set-up and nice to watch. A great addition to any fine piano to keep unwanted fingers off your keys.
This was a cool surprise! A mouse had made a nest under A0 and another one under C88. And there was lots of chunks of dog food stashed away. My dear Watson, this explains three things: the fat mouse; the skinny dog; and the piano owner who couldn't play the piano (because obviously they did not practice much.)