PicoLisp[1] And Shen Lisp[2] have included one in their std lib, and maybe Prolog-like implements core.logic[3] and POP-11[4], many minikanrens[5].

[1] https://picolisp.com/wiki/?home

[2] http://shenlanguage.org/

[3] https://github.com/clojure/core.logic

[4] https://en.wikipedia.org/wiki/POP-11

[5] http://minikanren.org/