"Why isn't there an Open Source, standardized, self-hosted, version of this kind of service? Or, why hasn't one, or two, options emerged that everyone uses and

"Why isn't there an Open Source, standardized, self-hosted, version of this kind of service? Or, why hasn't one, or two, options emerged that everyone uses and I would have heard of by now?" Because it is a lot of hard, strict and continuous work. Specially if you want - and you kinda need to, if you want anyone to use you - to provide customization for: styling, different databases, languages (both programming and natural), login methods (SSO, email, etc), email delivery systems, user fields, etc. So people building open source generally will just solve their own problem and might share that, not solve a problem space one up with all of these combination complexity mess. The most "standard" open source I know is Passport.js, but it only solves the problem of login methods.