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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.
KDE-Connect. I've been using it for a while and its great. It's open source, available on F-Droid (also pretty sure it's on google play) and baked directly into KDE. Also on other desktop environments but your mileage may vary. You can share the clipboard, files, get notifications, remote input, etc. It's also TLS encrypted from end to end.
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.