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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.
OBS - Screen-capping/screen recording software.
Technically, it IS open source (source here: https://github.com/aseprite/aseprite). However, it is licensed in a unique fashion. You are not allowed to redistribute it in binary (compiled) form, but you are perfectly fine to use it for free if you compile it yourself.
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.