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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.
There are also lots of "coding challenge" websites/services out there. Personally, I think the most fun and interesting one is Advent of Code.
NOTE:
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Hence, a higher number means a more popular project.