http://jyte.com/: it's kinda fun: you sign in with your OpenID and make claims about things (doesn't matter what) and vote on those claims. You can also give credit to other people, join and create groups and record contacts and relationships.
Sounds pretty standard, but what I find interesting is that there are a set of APIs for querying group membership. This could potentially allow an application to restrict access to an invitation-only group defined on jyte, and then only people who are members of those groups will be allowed through.
Another interesting area is the upcoming credit API; it will be possible to query the overall credit score of an identity. I'm wondering if a high enough credit score will be acceptable as "proof enough" that a user is not a bot, and that we could then remove the captcha step for those users.
It will be interesting to see where these concepts go as the year progresses.