GreenPass is a personal data management tool. It works like a personal diary book. Only the person owns it can put data into it. Nobody owns the data except the owner himself. This is ensured by the underlying blockchain technology. And this 'diary' is smart enough to show people you submit data on schedule and data quality is good (with green status), but never disclose any details to others without permission.
GreenPass is also a personal time management tool. It provides appointment service. Owner can set a free time schedule with location. Others can make an appointment.