Windows Workflow Foundation is the programming model, engine and tools for quickly building workflow-enabled applications on Windows. It consists of a Microsoft® WinFX® name space (System.Workflow), an in-process workflow engine, and designers for Microsoft Visual Studio 2005. Windows Workflow Foundation is available (currently as Beta) for both client and server versions of Windows. Windows Workflow Foundation supports a wide range of scenarios including workflow within line-of-business applications, user interface page flow, document-centric workflow, human workflow, composite workflow for service-oriented applications, business rule-driven workflow and workflow for systems management.
Introducing Microsoft Windows Workflow Foundation: An Early Look
Getting Started with Microsoft Windows Workflow Foundation: A Developer Walkthrough
Windows Workflow Foundation - Developer Center