This is a SCR controller and they exist for managing electrical power to things needing presise control or power factor correction. Notably heating elements and motors.
It’s on a standard DIN rail of the sort PLCs can also go on.
Opps, I got messed up because I read the 428 in the pic and registered that as the number instead of the 517 (things like this seem to happen when I only get 4 hours of sleep). Sorry about that...
Anyway, here's a candy crush level 519: