Ask HN: What are some good “starter” GitHub foss projects to contribute to

Personally, although I have decent development capabilities in a fair amount of languages, despite wanting to, I've never contributed to an open source project. The task of finding one suitable is somewhat daunting.

I imagine it's like going to the gym for the first time, daunting for the first week or so before you get into the swing of things and realise everybody wants you to succeed.

So, what are some good projects for diving into?