Unlambda is a "purely functional programming language" made by David Madore. It is based on combinatory logic. You can read more about it here: [http://www.madore.org/~david/programs/unlambda/](The unlambda programming lanugage).
This interpreter isn't complete, but it is usable. It supports the s, k, i, .x and v functions. The good part is that this interpreter can do abstraction elminimation, so you don't have to worry about it.
To use this interpreter, run it with java -jar Interpreter.jar -help, and read more there.
Note: the terminal version is VERY slow.