The Corona data donation project (Corona-Datenspende) is one of the largest citizen science projects worldwide in which over 100,000 people donate personalized, physiological sensor data (heart rate, physical activity and sleep) collected via fitness trackers and smart watches in a privacy preserving fashion. At the same time users take part in regular surveys about their current and past health status as well as their behaviour and experiences over the course of the COVID-19 pandemic. The scientific progress is made transparent on a regular basis via social media and a dedicated science blog that instigates discussion and interaction among the users and the involved researchers. Here, we showcase a variety of applications and insights that have evolved from this unique data set: (i) A nowcast system for COVID-19 case numbers from physiological data. (ii) A classification system for Long-Covid that shows the positive effect of vaccinations for mitigating long-term impacts on individual health. (iii) A large-scale analysis of human sleep patterns that shows pronounced geographical and socio-economic imprints. (iv) The overall positive relationship between physical activity, sleep and self-assessed well-being. Our results imply that digital projects like the Corona-Datenspende have the potential for engaging a large portion of the general public in addressing the contemporary challenges of our time. Due to its flexibility it simultaneously complements traditional methods such as field-work, clinical studies or surveys as data collection can be quickly adapted to new emerging research questions.