I am working on an open cookbook for Julia. It sits at http://julia.cookbook.tips/ . It should be complementary and not substitutional to the official Julia docs.
I would think the cookbook already has its moments. that is, it is already useful, but there are still a lot more questions than answers. I have been better at asking and organizing questions, and not in answering them, which has been mostly Pranav Bhat’s credit.
if you are interested in helping out, please drop me an email (firstname.lastname@example.org).