In this cross-disciplinary project senior citizens and researchers participated in the collaborative design and development of a mobile exercise application to prevent falls. The methods Form-IT and Participator) and Appreciative Action and Reflection (PAAR) were applied in a series of workshops, facilitating the creation of new knowledge and a socio-technical platform for an end-user development process. The participation of the older people was key to understanding the broad range of preferences and motivational aspects. The outcomes emerged into prototypes, which were composed using the ACKTUS platform for end-user development, resulting in a dynamic application, easily adaptable to future needs and studies.