Add to ORKGThis thesis deals with the problematics of designing, implementing and testing of mobile application for operationg systems iOS and Android. The main work of this thesis is development of an application, which allows its users to create challenges and invite their friends to participate in them. Users can also watch the progress of other participants in a challenge, which can give themselve more motivation to complete the challenge. The application was designed and developed with focus on opinions of its users. I have started by developing a prototype in order to find out, which functions do the users find the most crucial. Thereafter I created the first official version, which was subsequently iteratively improved with regard to feed...