FOSS 101: Great/hip open source projects Python/JS/Ruby

I'm an intermediate python programmer with very little JS / Ruby experience (want to learn both though)- and none with open source contributions. So far, that is.<p>Wondering if there any cool (ideally a bit faddish / trendy :) open source project people would recommend to start off my open-source contributions with. Ideally something that has the bureaucracy to review my code / give suggestions etc on how i cam improve my patches, and so i learn something in the balance!