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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.
It is based on Raspberry Pi OS, and because of that most of its components are open source. As for its own components, I was able to find source code for some of them - here is the updater for example. It's true that the site does look barebones though.
NOTE:
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