In 2010 Harry Walker developed arubric, and I used his rubric (with some modifications by Kathy Schrock) as the basis for mine. (Read Harry Walker's paper Evaluating the Effectiveness of Apps for Mobile Devices.)
I kept in mind that some apps are used to practice a discrete skill or present information just one time. Others are creative apps that a learner may use again and again, so it's a challenge to craft a rubric that can be used for a wide span of purposes. I tried to make my rubric work for the broadest range of apps, from drill and practice to creative endeavors, while stressing the purpose for using the app.
My rubric also emphasizes the ability to customize content or settings and how the app encourages the use of higher order thinking skills. Admittedly, there are good apps that are not customizable and focus on lower order thinking skills. Factor Samurai, for example, is a fantastic game for identifying prime and composite numbers. It would be nice if the app had flexibility to adjust difficultly, but it's still a good app if it is relevant to the learning purpose.