Ask HN: Open-source projects opened for beginners?

Hey guys and girls! I'm learning programming for some time now, I have job as Designer/Front-End Developer in small company, but I want to learn more by contributing to some open source projects. An ideas where should I start this journey? What are some good initiatives opened for beginners?

I'm mostly coding in Ruby and JS, but I'm not afraid to Python and I'm mainly interested in frontend things.