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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.
Use the reMarkable cloud via its API, using something like rMAPI
Connect the tablet to your computer, use a client program like RCU (which, yes, is paid but also open source) or Remarkable Assistant (free, open source, but old; probably still works)
If you want to understand the reMarkable's internal structure and its API access, the reMarkableWiki is probably the best place to start. You can also look around the Awesome reMarkable for interesting programs then look into those programs' code.
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.