Twitter and related services provide immediacy but little engagement (90% of users don't tweet). Facebook & apps are more conversational and engaging, but less immediate and limited to existing social relationships.
The participative web is a new generation of real-time services connected to real world activities, locations & events. They provide fun & useful ways to exchange information around immediate shared interests across social networks via intuitive visual interfaces and game elements with measurable rewards.
If you're developing a participative web application, I'd enjoy hearing from you at email@example.com.