Hunts for js files in a directory tree, and runs uglify-js on them in parallel (one per CPU).
Easily modifiable to run any job in parallel (see worker.js).
On an 8-core machine a large test takes 2.5 hours utilising a single CPU, and 20 minutes with parallel-uglifyjs.
$ npm install parallel-uglifyjs
$ ./parallel_uglifyjs small_test