Anecdotally, I feel like I've previously seen ShoutWiki Calendar used for tasks relating to this extension. Whether or not it should be used like that is a different question :)

It shouldn't. That's an unrelated codebase. T212165#10771377 was what made me finally file this, although it's been bothering me for a while.

Judging by https://phabricator.wikimedia.org/project/manage/620/#31187, it looks like - prior to being renamed to #ShoutWiki Calendar in December 2016 - the project was originally just #MediaWiki-extensions-Calendar/#Calendar. (So I guess my question would be, should it just be renamed back?)

Looking at all the tasks currently tagged with #ShoutWiki Calendar (https://phabricator.wikimedia.org/maniphest/query/gpw6kwmUEZqM/#R), all but one of them (T149402) actually relate to the Gerrit mediawiki/extensions/Calendar repository (which, judging by its extension.json file, is the repository for the Calendar-Wikivoyage extension).

I feel like there might be some historical reasons why things are currently the way they are, though I don't know myself what those reasons might be. Tagging ShoutWiki & ccing @SamanthaNguyen in case they know any of the historical context here :)

Ah, I think I might have found the context behind the tag being renamed: T154242#2905231

These two extensions seem to have been conflated from very far back. My guess is the current project labeled ShoutWiki Calendar was originally intended to be for the Wikivoyage calendar extension and was hijacked by SamanthaNguyen, probably without realizing she was doing so. Regardless, though, both calendar extensions deserve a project and so a new project needs to be created.

I would leave ShoutWiki Calendar alone (it's kind of too late to unwind now and would make histories confusing) and create a new MediaWiki-extensions-Calendar-Wikivoyage project. And the hashtags #calendar and #mediawiki-extensions-calendar shouldn't point to anything.

On its face, that sounds like a reasonable course of action to me. I'd say that (IMO) there might be an argument for pointing #MediaWiki-extensions-Calendar to a new Calendar-Wikivoyage tag, though; given that the extension's name in Gerrit is just mediawiki/extensions/Calendar. In addition, if/when a new project is created, the tasks relating to Calendar-Wikivoyage that are currently tagged with ShoutWiki Calendar should IMO be moved to the new project (for accuracy regarding which extension the tasks were about).

It might be worth waiting a short amount of time before going ahead with this idea, though, in case anyone from ShoutWiki has any thoughts and/or additional context they'd like to add :)

On the third hand https://www.mediawiki.org/w/index.php?title=Extension:Calendar&redirect=no is a redirect to a disambiguation page.