The world is becoming mobile. Which options exist for Drupal and mobile development? Actually there are three.
1. Mobile Web Apps
New web apps which are built with mobile devices in mind can be built with responsive design in mind, so that they will be available on all desktops and mobiles. This site is responsive - try to resize the browser window and see what happens.
mobile web apps will have a distinct advantage over native apps because they are cheaper and easier to maintain, decrease time to market and cross-platform compatible (Paul Chason)
2. Native Apps
Native apps take more time to create and cost more to maintain: We have to be built again for each opereating system (At leasto for iOs and Android). One time for iPhones, and the other for Android machines. For iOS, it's Objective-C, and for Android, it's Java. They are available for installation through the respectable app store. They have better performance.
3. Hybrid Apps
Hybrid apps take the best of both worlds. They use a native app wrapper to show a regular web app.
A hybrid app uses a native app “wrapper” to display data from an HTML web app. It’s downloaded and installed from an app store but still implements web functionality to a large degree. (Paul Chason)
For small projects, start with a Drupal-based web-app. Build you website using responsive design. Later, you will always have the option to wrap it as a native app, using an hybrid mobile devevelopment approach.