Windows Workflow is a relatively new technology from Microsoft that aims to help developers creating systems that involve long-running processes. In some respects it provides a subset of the functionality provided by products such as Metastorm BPM, but is missing features such as roles management and forms integration. Also, it is designed as a tool for developers as opposed to end-users and as such the runtime can be hosted in any application as there is no workflow engine application or service. It is therefore essentially up to the developer to determine how the runtime system will be hosted.

Windows Workflow could be used to develop a fully featured workflow/BPM system, but many of the features that Metastorm BPM delivers out of the box would have to be created by developers. The advantage is, however, that you can develop the application to exactly your needs, or reuse existing systems.