Some cognitivists think that [...] Other cognitivists think that [...]

Is there a test of the real world that could tell us that some of them are right and others think wrong? If not, what is the value of describing their thoughts?

It's clear to me that applied and normative ethics deal with real and important questions. They are, respectively, heuristics for certain situations, and analysis of possible failure modes of these heuristics.

But I don't understand what metaethics deals with. You write:

Metaethics: What does moral language mean? Do moral facts exist? If so, what are they like, and are they reducible to natural facts? How can we know whether moral judgments are true or false? Is there a connection between making a moral judgment and being motivated to abide by it? Are moral judgments objective or subjective, relative or absolute? Does it make sense to talk about moral progress?

I don't understand why, given the reduction of these questions to substance, they are nearly as important as the first two categories. In fact, some of these questions seem to me not to reduce to anything interesting. "Does it make sense to talk about moral progress?" seems a question about definitions - given an exact definition of "moral" and "progress", there shouldn't be any empirical fact left to discover in order to answer the question. And the part of the post that discusses the positions of various philosophers gives me a strong feeling of confusion and argument about words.

I expect your next posts will make this clearer, but I wish you had included in this post at least a brief description or example of a question in metaethics that it would be useful to know the answer to. Or, at least, interesting to a reasonably broad audience.