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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
I stumbled upon "wger" or Workout Manager. It is an open source platform you can host that provides a bmi tracker, diary and exercise program. Each client could be set up as a user, but I do not know if you can access and track user's progress which would be important. https://github.com/wger-project/wger
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