Design Facebook Messenger.

Focus on the core functionalities that make Facebook Messenger a compelling communication tool. Consider user needs such as messaging, voice and video calls, and media sharing. Discuss how to ensure a seamless user experience across platforms (mobile and web), and think about scalability and performance. Address privacy and security features, as well as integration with other Facebook services. Finally, be prepared to outline your approach to user feedback and iterative design to enhance the product over time.