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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 personally use Strawberry, it's a fork of Clementine which stopped receiving updates in 2016. I mainly love how customizable it is.
The player is not open source but the skin is: https://github.com/kbuffington/Georgia
NOTE:
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Hence, a higher number means a more popular project.