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WCF is a new communication subsystem to enable applications, in one machine or across multiple machines connected by a network, to communicate.
WPF is the graphical subsystem feature of the .NET Framework 3.0 and is directly related to XAML.
WCS is a framework developed by Microsoft which securely stores digital identities of a person, and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website.
WWF is a Microsoft technology for defining, executing, and managing workflows.