A friend of mine at DeNA (Japanese mobile gaming company) spends most of his time at the office working on open source projects. Right now he's working on a language built on top of Javascript called JSX for large scale Javascript apps.

I did an interview with him a few months ago if you're interested: http://jhackers.net/Kazuho_Oku.html

(come to think of it, every programmer I've interviewed so far on above site works on OSS projects for work to one degree or another)