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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.
explain-pause-mode is also worth mentioning.
Some people also like gcmh and disabling GC in the minibuffer, which is what Doom does.
Granted, Flycheck makes it easier to create checkers. But flymake-collection and the macros it defines make it easier for Flymake.
NOTE:
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Hence, a higher number means a more popular project.