Some of the self-hosted options presented during sign up include Keycloak, Ory, Gitea, Zitadel, Authelia, and more.
There's also a workaround to create a passkey account by signing up with any SSO provider, inviting yourself as an external user, accepting that invite and sining in with a passkey, then leave the original SSO network. Then you're not tied to any external service at all.
https://news.ycombinator.com/item?id=22760130
> (I'm a Tailscale co-founder) The idea is to avoid building yet another commercial service that holds onto your username and password. People have enough identities already. More details here: https://tailscale.com/blog/how-tailscale-works/ We know we keep getting feedback that people want a different way to authorize their accounts (especially for personal use), so we're looking at other options. We just really want to stay out of the username+password business; it's simply bad security practice.