I often get the Question: “What is CardSpace?”
While there is a whole philosophical side to CardSpace (or similar products) – the technical and pragmatic answer is:
“CardSpace is a graphical client for security token services built into Windows”
(or as Keith recently said: “home realm discovery the nice way”)
Related questions are:
What is a card?
“A card is a graphical representation of the configuration details how to talk to that security token service (address, required claims, credentials and more…)”
Then what’s the difference between personal and managed cards?
“Personal cards use a local (aka personal) STS. Managed cards a third-party/remote STS”