"Consider that they allow visitors to post questions and answer, edit other people's questions and answers, and even query the database for any info that's public (e.g. not user passwords, but pretty much anything else), all without having an account."
This is not unique. Wikipedia's Reference desk[1] allows asking/answering any question by anyone -- even unregistered users.
Does anyone use it? By some combination of skill and luck, stackoverflow was clearly better positioned to fill this role, at least for software related content.
This is not unique. Wikipedia's Reference desk[1] allows asking/answering any question by anyone -- even unregistered users.
[1] - https://en.wikipedia.org/wiki/Wikipedia:Reference_desk