My broad image of what the plan would look like is something to the effect of:
Build a website whose main page consists of a large table of mappings from company names to EA subgroups within those companies, sorted alphabetically for ease-of-browsing. Then there are two branches currently coming to mind for how to gather information into the table: either a second page consisting of a submission-form for “here’s some new information to add to the table”, or wiki-style editing of the main page.
Then the first difficult hurdle: there needs to be some sort of moderation / fact-checking in place on the user-submitted data, in order to avoid problems with trolls submitting fake information, plus ideally also to avoid problems with its listings going stale. The wiki route is somewhat more accessible-to-editors, which on the one hand means staleness will be less of a danger but on the other hand means trolls will be more of one; but either way there are likely to be nonzero problems on both fronts, if the list gets at all big.
And then the second difficult hurdle: making the people who might benefit from the list aware of its existence. In one prong, this means search-engine-optimization; in another prong, this means posting it on the EA Forum; in a third prong, this means finding people who curate lists of EA-resource-links and letting them know about the list as a thing-that-exists-and-might-be-worth-linking; and plausibly there exist additional relevant angles that I’m currently failing to think of.
If I were working on this purely by myself, I’m reasonably confident that I could do the basic “create website and stick it at a URL somewhere” step, and plausibly I’d be able to figure out the search-engine-optimization and the spreading-word-of-its-existence. (Post on EA Forum, post on the EA Discord channel I’m in, mention its existence to friends who might know of other good places to post about it, et cetera.) However, I feel pretty much entirely inadequately-equipped for the task of moderation-of-user-submissions-to-the-list. So I suppose that’s my big bottleneck, currently.
(Also important, on the side, is ensuring reasonable initial seeding of listed companies. Ideally people would be able to look at the list and see both Big Companies With Huge Numbers Of Employees and smaller startups, because otherwise I worry the list would end up with only people in one of those company-types submitting information to the list, on the assumption that the other type is Not The Target Audience, and that’d produce a list-usefulness-reducing feedback loop. I myself work for a single big company, but ideally I’d want to accumulate ~10 initial list-entries of varied company-size prior to posting about the list too much in the broader social sphere, so that most people’s first impressions of the list would end up being of its being already-seeded.)
Ooh. This does, indeed, look like pretty precisely the sort of thing I was envisioning, yes! Albeit less search-optimized than ideal, I think, in light of how I failed to find it even when actively running searches for e.g. “effective altruism at tech companies” in my first pass at trying-to-locate-prior-work-before-resigning-myself-to-doing-the-thing-myself.
Still, this sure does seem like pretty solid prior work in the field! Enough that I will likely pivot over from “try to build the thing myself” to “try to figure out how to improve the preexisting thing”, at least for the time being. Thanks for the pointer!