During the past years we have been discussing and iterating over our mobile application architecture at Karumi, and the result of all that work is called Rosie. Rosie is a framework that helps application development by focusing on three pillars that we consider very important: testability, code scalability y code readability. This talk is not about promoting Rosie but rather the creation process of this framework, the needs that we needed to cover and how we materialized all the literature present in tons of books and internet articles. This is about problems and solutions Rosie is a framework that helps application development by focusing on three pillars that we consider very important: testability, code scalability y code readability. We show the internal code and we talk about the design considerations.