Windows CardSpace
Windows CardSpace was developed by Microsoft as a program for the Identity Metasystem. CardSpace was used to create digital identities for users, storing some personal information about them that could be requested and accessed by websites or other software applications. Users could also create personal cards, utilizing up to 14 fields to store information.
When users' information or identity was requested, the CardSpace UI (user interface) would appear, looking somewhat like a business card or Outlook Contact with information about the user. The user can select what card to make available to a website or application, which results in the website or application requesting a digitally signed XML (extensible markup language) token. This token would then contain the information being requested about the user.
Microsoft originally included Windows CardSpace with the .NET Framework 3.0, designed to run on Windows XP, Windows Vista, and Windows Server 2003. It is installed by default on Windows Vista and Windows 7, and can be downloaded for Windows XP and Windows Server 2003 for free. Microsoft has since discontinued Windows CardSpace, putting time and resources into developing a replacement called U-Prove.