Windows CardSpace was developed by Microsoft as a software 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 also had the ability to create personal cards as well, utilizing up to 14 fields to store information.
When users' information, or identity, was requested, the CardSpace UI 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 token. This token would then contain the information being requested about the user.
Microsoft originally included Windows CardSpace with the .NET Framework 3.0, which was 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, opting to put time and resources into developing a replacement call U-Prove.