Many, many species of plants are inbreeders. In the plant world, inbreeding and outbreeding seem to both be successful techniques with their own benefits and drawbacks.

If I remember correctly, certain types fruit flies prefer inbreeding.

Royal consanguinity marriages in old Europe. And many other places as well. Sibling marriages in Egypt and the Diadochi!

Ancient Ireland, too: https://www.newscientist.com/article/2246227-stone-age-rulin...

When they do it deliberately with cattle they call it line breeding.

Many show breed dog pedigrees have lots of ancestors, many of them the same dog.

Have you heard about the Fugate family from Kentucky?