You could be forgiven for not knowing what the heck these are for:
That's a knife specifically designed for mushroom foraging. The bristles are to clear debris to expose the stem for slicing, and to dust off the cap. The versions above and directly below are made by Italian manufacturer Maserin, whose wares we previously checked out here.
This one from Garrett Wade features a more legible sizing scale and a tiny compass embedded in the handle.
Swedish manufacturer Morakniv reckons their form factor is more ergonomic than the incumbent form:
That's about all the design variation we found--most them resemble the Garrett Wade, with slightly different handle shapes--though there's dozens of manufacturers of these things. If you're curious about their use, food writer Susan Grey has a mushroom knife explainer on her Grow Your Pantry blog.