Yes, you can write a Dart program on Replit that runs on mobile and web browsers. Dart is versatile and used for mobile app development with Flutter and web development with frameworks like AngularDart. Replit supports Dart, allowing you to develop both mobile and web applications directly in your browser. For mobile apps, you may need to use an emulator or connect your device to test. For web apps, you can preview in Replit or deploy to a hosting service for access on the web.