An OpenID is a single username and password that lets you login to any site that accepts an OpenID. Having an OpenID means you don't have to remember a username and password for each individual site you visit but a site is still able to conclude you are a valid person by making you confirm via email you are who you say you are.
We've gone ahead and implemented OpenID so if an Inkling marketplace manager turns it on, you now have a choice of how to sign in to any Inkling marketplace: your OpenID or a traditional username and password generated by Inkling. We've turned it on for our public marketplace so everyone can see how it works.
Also, for organizations wishing to do "single sign-on," OpenID is an interesting alternative to consider. However, we will always still offer our web service which allows organizations to easily use their own authentication system for their users logging in to Inkling.
If you don't already have an OpenID and want to try using OpenID on Inkling or other enabled sites, just visit the directory of OpenID providers (it's free to get one) or use the provider we use: MyOpenID.
UPDATE: a quick update on our Inkling pilot program. We now have close to 60 trial marketplaces up and running. They continue to be a mix of big business, individuals, and academics. We are very happy we decided to open this up as there is clearly a demand to see just what running a prediction marketplace yourself is all about.