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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've seen two free and open source AirPods apps for Android, Pods Companion and CAPod. Some people definitely make completely free apps as a passion project. I haven't tried these since I don't own AirPods but they seem pretty good.
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.