Games nowadays work as an undivided part of the teaching and learning process. Especially when they are combined with mobile devices increase the level of motivation and interest. This paper presents the design and creation of an AppInventor application that utilizes mobile devices and is addressed to junior high school students. Through this application, the students are invited to learn basic mathematics concepts aiming to improve their knowledge, perception and attitude towards Geometry. The developed application, which is called "Pythagorean Academy", follows the teaching instructions and the proposed curriculum for the course of mathematics of the Greek Institute of Educational Policy and the Ministry of Education and gives students the opportunity to assimilate the taught material and to enrich and interactively test the knowledge they have acquired.