Recently, global tech companies released so-called virtual intelligent personal assistants.This thesis has a bi-directional approach to the domain of spoken dialog systems. On the one hand, parts of the work emphasize on increasing the reliability and the intuitiveness of such interfaces. On the other hand, it also focuses on the design and development side, providing a platform made of independent specialized modules and tools to support the implementation and the test of prototypical spoken dialog systems technologies. The topics covered by this thesis are centered around an open-source framework for supporting the design and implementation of natural-language spoken dialog systems. Continuous listening, where users are not required to signal their intent prior to speak, has been and is still an active research area. Two methods are proposed here, analyzed and compared. According to the two directions taken in this work, the natural language understanding subsystem of the platform has been thought to be intuitive to use, allowing a natural language interaction. Finally, on the dialog management side, this thesis argue in favor of the deterministic modeling of dialogs. However, such an approach requires intense human labor, is prone to error and does not ease the maintenance, the update or the modification of the models. A new paradigm, the linked-form filling language, offers to facilitate the design and the maintenance tasks by shifting the modeling to an application specification formalism.