Windows Workflow Foundation

>>Windows Workflow Foundation (WF) is a Microsoft technology for defining, executing, and managing workflows. This technology is part of .NET Framework 3.0 which is available natively in the Windows Vista operating system, and can be installed on the Windows XP SP2 and Windows Server 2003 operating systems.

Authoring Workflows
A new XML-based language XAML is commonly used for declaring the structure of a workflow. However, the workflow may also be expressed in code using any .NET-targeted language (VB.NET, C#, C++/CLI, etc.).
Workflows comprise 'activities'. Developers can write their own domain-specific activities and then use them in workflows. WF also provides a set of general-purpose 'activities' that cover several control flow constructs.
Windows Workflow Foundation is supported by a companion set of extensions to Visual Studio 2005. These extensions contain a visual workflow designer which allows users to design workflows, a visual debugger which enables the users to debug the workflow designed, and a project system which enables the user to compile their workflows inside Visual Studio 2005.

Moving data through Workflows
Activities that require or provide data can use properties to expose them, and enable the Workflow author to bind them to the containing workflow by declaring 'dependencies'.

Hosting Workflows
The .NET Framework 3.0 "workflow runtime" provides common facilities for running and managing the workflows and can be hosted in any CLR application domain, be it a Windows Service, a Console, GUI or Web Application.
The host can provide services like serialization for the runtime to use when needed. It can also hook up to workflow instance's events such as their becoming idle or stopping.

Communicating with Workflows
WF workflows define interfaces with methods and events to communicate with the outside world. A host application typically sets up an environment before running a workflow, providing objects that implement those interfaces.
When an object implementing such interfaces raises an event, the corresponding workflow is retrieved and the data passed on to it.
Methods on the interface may be used by the workflow to communicate with its host. Data can also be transferred from the host to the Workflow through dictionary objects that are passed to the Workflow when the Workflow is created.Similarly the Workflow can pass the results of the workflow to the Host application through a Dictionary Object.
The WorkFlow foundation also allows the Workflow to update the Host application of the progress of the workflow. this is done by raising events in the Workflow to which the host application will subscribe.

>>List of Microsoft Windows application programming interfaces and frameworks
Active
Active Scripting
Collaboration Data Objects (CDO)
Component Object Model (COM) including ActiveX, ActiveX Data Objects (ADO) and Distributed Component Object Model (DCOM)
Cryptographic Application Programming Interface
DirectShow
DirectX, including: Direct3D, DirectDraw, DirectInput, DirectMusic, DirectPlay, DirectSetup, and DirectSound
Graphics Device Interface (GDI) and GDI+
Extensible Storage Engine (Jet Blue)
Microsoft Data Access Components (MDAC), including: OLE DB
Messaging Application Programming Interface (MAPI)
Object linking and embedding (OLE), OLE Automation
Remote Application Programming Interface (RAPI)
Speech Application Programming Interface (SAPI)
Telephony Application Programming Interface (TAPI)
Uniscribe
Windows Image Acquisition (WIA)
Windows Management Instrumentation (WMI)
Winsock
Win32 console
Windows API's current versions: Win32, Win64

Deprecated
Collaboration Data Objects for Windows NT Server
Dynamic Data Exchange
Older data access technologies: Microsoft Jet Database Engine, Data Access Objects (DAO), Remote Data Objects (RDO), Remote Data Services (RDS)
Setup API
Windows API's old versions: Win16, Win32s