A prying tool, not a cutting tool: short, thick, and rigid. The oyster knife is essentially a lever, built for toughness rather than edge retention. The tip is inserted at the hinge, the blade is twisted to pop the hinge muscle, then the shell is lifted and the The strong muscle that holds the two halves of the shell shut; cutting it frees the meat from the shell is cut to free the meat.
Because it works by leverage rather than slicing, the blade stays comparatively dull on purpose. A keen edge would only invite the slips and punctures that make shucking the most injury-prone job in the kitchen.
Primary tasks: shucking oysters and opening clams. The clam knife is wider and more rounded, and the technique differs (a sawing entry rather than a straight pry).
Safety note: a hand guard or chain-mail oyster glove is strongly recommended, because the hand holding the shell is always in the path of the blade.
Limitations: strictly single-purpose. It is not used for any general kitchen cutting task, and its short, thick blade makes it useless for the slicing and chopping the chef's knife or paring knife handle. Care here is mostly about rust prevention rather than edge maintenance.