Extending Windows Workflow Foundation
The following section describes how to extend Windows Workflow Foundation (WF) with custom activities and designers in rehosted environments outside Visual Studio 2010.
Customizing the Workflow Design Experience
Indicates how the scenarios for designing custom activities and for rehosting the Windows Workflow Designer have been greatly simplified in .NET Framework 4. Development and deployment are now both easier and more flexible because the new activity designer programming model is built upon Windows Presentation Foundation (WPF).