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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.
Prepare to spend a fair bit of time reading and going back to phptherightway.com and php.net. I've also found this Tutorial from Envato Tuts+ to be quite good.
NOTE:
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Hence, a higher number means a more popular project.