Y-erlang is a project mainly written in ..., it's free.
using erlang to learn about the Y-combinator, and vice-versa
This is just a toy I was playing with this afternoon: I was intrigued by Mike Vanier's explanation of the Y combinator in scheme at http://mvanier.livejournal.com/2897.html, and since I've been using erlang lately I thought I'd try out the concepts in another language.