Well, you can keep 3 Dwarf Mexican Crayfish in a 10. They're pretty simple, but definitely look up care requirements anyway. They do have a few specialized needs.
Otherwise, you're a bit limited on freshwater crabs. The only ones I can think of are Thai Micro Crabs and Freshwater Pom Pom Crabs, and I've never heard of either doing super well for long periods of time. Micro Crabs will be almost too tiny to keep track of in a 10, and Pom Poms can be sorta hard to get.
If you're willing to get a bit salty (brackish, actually) you can do a single Red Claw Crab in a 10. They do require some land in their tank, as well as brackish water, but care is pretty simple other than that.
If none of those really pique your interest, you could always do a shrimp tank. If you're not a fan of the usual varieties (Cherry shrimp, ghosts, etc.), look into wood and bamboo shrimp. They're filter feeders, so, again, special care, but they're definitely different and more crayfish-like.
The only other inverts that I could think of require saltwater, so unless you're into that (and prepared for it), choices are a bit limited.