WF - Quickly Build Workflow-Enabled Applications on Windows
Windows Workflow Foundation provides a declarative way of writing an application or algorithm and can be used to implement complex processes. WF includes a default set of activities that provide functionality for control flow, conditions, event handling, state management, and communicating with applications and services. When you design workflows, you can use the activities that are provided by Windows Workflow Foundation, and you can create your own custom activities.
Activities are the fundamental building blocks of workflows. A workflow is a set of activities that are organized hierarchically in a tree structure. An activity represents an action in a workflow. It can be a simple action such as a delay, or it can be a composite activity that consists of several child activities.