This page holds an Unlambda interpreter I've written in C.
Unlambda is an obfuscated functional programming language invented by David Madore, strongly based on the lambda calculus. The S and K combinators are the core of the language, which suffice to make it Turing complete. Moreover, it has the powerful call with current continuation function (found in very few languages, notably Scheme), a special form to delay the evaluation of expressions, and some other handy functions to print and do input.
The full documentation can be found at: