"Lazy K is a garbage-collected, referentially transparent functional programming language, with a simple stream-based I/O system.". That is the short description of the language, given by its creator - Ben Rudiak-Gould. This language is much more minimalistic than unlambda - it has only three predefined combinators: S, K, and I (you can't define your own combinators).

More info in document hosted at http://homepages.cwi.nl/~tromp/cl/lazy-k.html