From out of left field comes a federated identity scheme called TypeKey. Developed by SixApart, TypeKey is designed to reduce weblog comment spam, an increasingly difficult problem. Most interesting is SixApart’s comments on other uses of TypeKey:
We’ll be providing documentation on how to integrate TypeKey authentication into your own applications shortly after the service launches. At that point, there will also be information about what is required to make use of TypeKey services in commercial applications.
FYI, this weblog runs on SixApart’s TypePad service.