Major depression is regarded as a significant and serious disease with an increasing prevalence worldwide. However, not all individuals with depressive pressive symptoms seek help for their problems. These untreated "hidden" individuals with depressive symptoms require the design and dissemination of evidence-based, /ow-cost and scalable mental health interventions. Such interventions provided by mobile applications are promising as they have the potential to support people in their everyday life. However, as of today it is unclear how to design mental health applications that are effective and motivating yet non-intrusive. In addressing this problem, the MOSS application is a recent endeavor of a Swiss project team from Universitiitsspital Zurich, ETH Zurich, University of St. Gallen and makora AG, to support people with depressive symptoms. In particular, evidence-based micro-interventions are recommended and triggered by individual characteristics that are derived from self-reports, smartphone interactions and sensor data. After one year of development, the study team now conducts a first empirical study and thus, recruits people affected by depressive symptoms to improve not only the application as such but with it, the delivery of mental health interventions in the long run.