This is a Promises/A+ implementation that I wrote for fun.
On top of what's defined in the spec, I also added some of the modern goodies like the constructor API, .catch, and the static .resolve/.reject/.all methods.
To run the Promises/A+ test suite (and a few of my own):
git clone https://github.com/scwood/simple-promise
cd simple-promise
npm install
npm test