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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.
April is the implementation I got started with and it is the reason I am not moved by Daniel's "drawbacks." But April isn't optimized and it isn't battle-tested.
Others like ngn-apl and dzaima/APL don't seem to be widely used and/or are not actively maintained.
Co-dfns feels like an academic project that I won't be able to figure out how to use.
BQN is too new for your criteria, but it's got more hype than any APL family language in recent memory. I'd be interested to see how it fares in a few years.
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.