Web applications, mobile applications and progressive web applications are the three main types that can be used in smartphones today. These have multiple pros and cons and the decision about which type to choose must be made before the start of the development. When developing a mobile application, the developer should take into account at least two operating systems: Android and iOS. This can be achieved by either building two native applications or by using a framework or development kit that allows the creation of the two version with only one source code. The purpose of this thesis is to build an application that answers the management needs of a nail salon in Switzerland such as appointment management and storage for client in-formation. As the app should be available in iOS and Android, it will be built using Flutter which is a development kit created by Google that uses Dart as its main language to build the application. The back-end part will be created using Firebase which can contain the database and numerous functionalities that will be discussed later during this thesis.