As we move off of Angular, Rhapsody's architecture needs to evolve to support the large and ever-growing amount of code that it will need to support. One large aspect of this is inverting how Rhapsody the platform runs and displays domain-specific code (the Dialer, settings pages, nav icons, etc.). The app registry is the mechanism by which domain-specific code will register itself to be run and displayed by the platform.
Be on the lookout for future updates regarding different aspects of the application using the app registry.