uLISP
The language God would have used to implement the Universe. — Svein Ove Aas, Road to Lisp

So what is this

An absolute bare minimum LISP interpreter written in ANSI C. It was developed to have an extremely small footprint and to be easily portable. Besides that, it has some pretty neat features:

How does it look like?

This example computes the value of 5! (five factorial) and prints it
(define fac
  (L (aa b)
    (let (a (if (== aa 0) 1 aa))
      (if (== b 1) a (fac (* a b) (- b 1))))))

(println (fac 0 5))

Ok, where can I get it?

As of now, only using SVN: https://hs.32leaves.net/svn/uLISP (WebSVN is here). Username and password is guest

Is there any documentation?

Some rather rudimentary reference documentation exists. It's also within the source tree.