More generally, it might be thought to include corkscrews used to remove cork or plastic stoppers from wine bottles.
The functional elements of bottle openers (a tooth or lip to catch the underside of the cap, a fulcrum across which to exert the force that will remove the cap, and usually a lever for mechanical advantage) tend to be consistent, although they can vary in design and aesthetics.
But as well as being portable it also comes as a fixed device to be attached to vertical surfaces, often with a tray to catch the bottle tops.
Carried in the pocket or against the body or on a zip string, it is both convenient and fast for the modern bartender.
Works the same as the lever variation, except that it is attached to the wall, to allow for simpler bottle-opening, which can be done with one hand.
[1] Two ophthalmologists Cam Loveridge-Easther and Sacha Moore wrote a letter recommending for warnings to be put on bottles.