A ten gallon makes for the perfect betta tank, if you’re liking the idea of fish! I don’t think it’d be big enough for hermit crabs, or at least not after a while. But you could probably do some sort of aquatic crab, there’s several species that stay small, though I don’t know them off the top of my head and I’m unsure what kind of specific care/space requirements they have. You could potentially keep a male kenyan sand boa, since they tend to stay so much smaller than females. Or a single male mouse could be comfortable in a ten gallon as long as you’re willing to spruce it up a bit and give him lots of climbing things and whatnot. There’s a few types of small frogs you could look into, or house geckos. Or something like snails or a tarantula or other inverts would be good too. And of course you could always use it as a grow-out tank for a number of baby animals with the idea of upgrading them as they grow.
African dwarf frogs. They’re a fully aquatic frog species with a body length of about an inch, and their care is almost identical to fish. The only difference is you have to be sure they can access the surface of the water to breathe air. You could keep several in a tank that size, and they’re cute little guys. Just be sure you get an african DWARF frog and not a clawed frog, clawed frogs get big.