I recently stumbled upon this OSS project while looking into CGM (Continuous Glucose Monitors). It's extremely feature-full, aggregates data from many types of glucose monitors, and provides open interoperability hooks for other tools. It even uploads the data to Google Health/Fit if you request.<p>It's a labor of love, created by the Nightscout Foundation - a bunch of folks who wanted to make life easier for family members who have Type 1 diabetes.<p>It's been developed for years. It's open-source.
It's free as in beer. It supports interoperability of data or other additional good-for-the-commons aspect. It has medical or other direct impact on QOL of some group of people.