Google Accounts consumer edition
Identity Provider
OpenID - Publicly available, see docs
Google Apps Premium Edition
For interop testing, we suggest registering a new domain at www.google.com/a. Once the domain has been created, you can also signup for the 30 day trial of the premium edition which offers the SAML RP feature. If you need access to the feature for longer then 30 days, then you can either pay the small monthly fee, or contact Eric Sachs at Google to have your domain upgraded for free, however it may take a few days and you can only use that domain for testing purposes.
Relying Party
SAML-Publicly available, see docs.
Identity Provider
OpenID-Available in production, but not yet formally announced because we want to do more interop testing. Currently it only works for FREE domains hosted by Google Apps, and not for domains that are trying, or paying, for the premium features. Therefore interop participants may need to use one domain for SAML RP testing, and another for IDP testing. However if you contact Eric Sachs he can have this feature turned on for an upgrade domain, however it may take a few days. This OpenID identity provider operates almost exactly the same way as the consumer one (see docs). However the one key difference is how discovery is handled to start the process, so we have seperate docs for that aspect.
SAML-We started making this available for interop testing in late June. It is a very simple SAML IDP whose purpose is to enable us to start interop testing and decide what the minimum features are that we need to support to be worthwhile. See the draft docs for this IDP.