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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.
UrBackup - https://www.urbackup.org/ again, more complex to set up - requires a client/server relationship
Syncthing - https://syncthing.net/ will do nicely for you. You'll need to install it on both your NAS and your PC then limk them together.
NOTE:
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Hence, a higher number means a more popular project.