I was looking through the tags, and came across grammar and grammaticality, and reading their wiki's I noticed they mean almost exactly the same thing. Based on my experience on other SE sites, I believe these are synonym tags, and should be combined.
The tag wikis are
Grammaticality - Grammaticality refers to whether something obeys the rules of English grammar.
Grammar - This tag is for grammar questions, including those about word forms, verb phrases, and such.
I think both descriptions are too vague. My understanding is that "grammaticality" is used when the question is not "Is this good English?" but rather "Is this grammatical, even though it might not be commonly used or awkward?", and that "grammar" is for questions regarding the rules of English grammar, like verb tense agreement with mass nouns or something similar.
I will give it some thought and see if I can suggest some verbiage that makes it clearer which tag should be applied to which type of questions. I think "grammaticality" is a subset of grammar, and that it is useful to have a more specific tag. I personally don't care for the "grammar" tag much - I'd rather see "verb-tense" or "pronouns" or something more specific.
How about these tag descriptions?
Grammaticality - This tag is used for questions asking if a construction is grammatically correct without regard to whether the construction is considered the common or accepted way to express something.
Grammar - This tag is used for questions asking about the rules of English grammar when it's not clear which more specific tag to use.