Pageflow is based upon Workflow Foundation, and can be used to drive user interfaces. It has it's own workflow type and on every transition (movement from screen to screen) activity additional work can be done between the transition from one 'screen' to another 'screen'.
It can be used with ASP.NET or WPF.
Pageflow was initialy developed by Matt Winkler.
All additions we've done on pageflow will be submitted towards the codeplex source.