I guess "PIP" fits into this category. It's been in beta about as long as OpenID has been a term. I used it for a several years before finally giving in an using my Google Account for everything.

https://pip.verisignlabs.com/

EDIT: Oh.. it's now Symantec, and they will no doubt try and sell you their other products :( ... well at least it used to just be an identity provider.