If you haven't heard of Travis CI before, it's a continuous integration service for open source* software. They currently support ruby, erlang, php, clojure, and node, with more languages in the pipeline... and more already working sans first-class support.

To abuse a phrase, this is the opposite of selling sugar water. It's set to revolutionize the already high quality OSS scene.

* - a planned feature is to support private, non-OSS projects

EDIT: moar languages than I thought!