Learning Elm in 2018: Comprehensive List of Resources

Learning a niche language like Elm involves a lot of head scratching over sparse documentation, posting to forums and hoping to get at least one response, looking at other people's undocumented code on GitHub to solve your problems, and generally a lot of stabs in the dark. Right? Well, I'm happy to say that at least for Elm, it's no longer true.
The official introduction to Elm is a useful overview of the language, but what's available beyond that? In 2018, the answer is "quite a lot", as it t...