https://www.fiskars.com/en-us/gardening-and-yard-care/produc...
Geared hinges https://www.select-hinges.com/products/geared-continuous/con...
But that is what's happening. That's what the gears are for. They synchronise the motion by transmitting force from either side to the other.
If the left leg faces less resistance (or has a stronger muscle, etc.), then the extra motion that would go into the left leg is instead balanced across to the right leg through the gears.
Intermeshing teeth I would think. What else are you going to call it? gear-like mechanics maybe.
Well, there are also oval gears, many types of non-circular gears, and so on. Not all cyclical/360 degree, e.g:
https://ae01.alicdn.com/kf/HTB11B0bhviSBuNkSnhJq6zDcpXaG/400...
A gear is about the teeth and the ability to synchronize according to a ratio. If you just need 180 degrees of motion (and e.g. will move it manually or automatically back to the starting point begin with), it's still a gear.