It looks like the primary differentiator from most other similar frameworks is the programmatic configuration and the inclusion as part of the Spring project itself.
From the project home page:
Spring Web Flow is a core module of the Spring Framework that is a strong fit for web applications with demanding page flow requirements.
The system lets you capture a logical page flow as a self-contained module that can be reused in different situations in a consistent fashion. The system is ideal for web applications that execute business processes over a series of steps spanning HTTP requests, and those demanding wizards, dynamic flows, and/or flows whose executions need to be audited or annotated. The system exists at a higher-level of abstraction, building on base Model 2 frameworks like Struts and Spring MVC, capturing your application's page flow explicity in a declarative fashion.It's only available via CVS, but might merit a look even at this stage.
Further recent changes, from Spring Web Flow Updates per TSSJS:
- Flow event processing is now fully decoupled from the HTTP servlet API.
- A FlowExecutionContext object has been introduced.
- Support for conditional transitions.