There are other animals that fit this description, but dogs are the only ones that also happen to reproduce fast enough that you could feasibly notice the improvement in behavior over generations.

In soviet russia, an experiment was made to see if the domestication of dogs could be replicated on foxes, with mild success. Basically all foxes in western Europe today are in some way crossbred from the tamer foxes produced by this experiment, explaining why foxes aren't completely terrified of humans.