The WF designer as used in VisualStrudio2005 can be re-hosted in other WinForm applications. See http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnlong/html/WFDsgnRehst.asp for more details.

Using the designer end users can modify/create workflows.

Note that the designer was originally designed for developers so leaves something to be desired for end users. Although a lot can be done not everything is possible. Most notable adding custom properties to workflows and adding code. Also some UI parts, like the compensating/fault view, cannot be be changed or removed.

See also WorkflowView, DesignSurface and WorkflowDesignerLoader.