As others have explained the Benaphore is a speed-up for an existing OS primitive, but the futex is a new primitive that's often much better suited to the problem you have. Benoit Schillings uses this name "Benaphore" but never claims explicitly to have invented it in the article naming it, either way though Benoit worked for Be Inc. which were making an entire OS including its kernel, so they could have provided the better primitive. But they didn't, BeOS provided the limited semaphore primitive you'd have seen in a typical 1980s or 1990s Unix.
Given that primitive, the Benaphore is a good way to use it, like if you've got a 1930s refrigerator and you've got a clever technique to reduce frost build-up - a modern fridge has a smarter controller and so it'll just defrost itself anyway automatically, no sweat. The Benaphore is thus redundant today - like that anti-frost technique for your 90 year old fridge.
Given that primitive, the Benaphore is a good way to use it, like if you've got a 1930s refrigerator and you've got a clever technique to reduce frost build-up - a modern fridge has a smarter controller and so it'll just defrost itself anyway automatically, no sweat. The Benaphore is thus redundant today - like that anti-frost technique for your 90 year old fridge.