Most of what I do day to day is web applications with Ruby/Rails. I'm looking into picking up a new language or two for fun (so far toyed with Scala, Clojure, and Haskell), and I find I learn the concepts best when I put it all together in an actual project. I'm not so interested in more web stuff or challenge-based things like Project Euler / CodeEval.
What are your favorite micro-projects for picking up a new language?
