Traditional workflow systems are not suited for highly interactive online systems. We present a state machine based workflow system, named FlexFlow, which formally describes Internet applications using statecharts. The FlexFlow engine uses these descriptions to directly control the execution of web applications. FlexFlow helps in generating controls for user interactions on web pages. Different versions of an application can be generated by visually editing its FlexFlow description, with minimal incremental effort in rewriting application code or related web pages. FlexFlow provides an efficient way to customize online systems and supports different versions of business processes in the same e-business system for different sets of industries, organizations, users, or devices. We demonstrate FlexFlow’s use for rapid prototyping of business processes and describe how we have used FlexFlow in commercial platforms for B2B e-commerce.