The aim of this thesis is to develop a web and mobile application using the Firebase Cloud Messaging (FCM, which allows sending messages at no cost. As an example, an gym application is created, which offers its clients the possibility of scheduling group trainings with receiving notifications an hour before the scheduled training. The client part of the web application is implemented using the Angular Framework, while the server part is developed using the Express Framework. The mobile application is made exclusively for the Android operating system.All data is stored in MongoDB.