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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.
There are many third party APIs handling interactive features (which is nice online) but if you just want simple, static Sankey diagrams with no external dependencies, https://github.com/ricklupton/floweaver looks 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.