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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.
Vala is not very widely used, but all applications in Elementary OS are written in Vala, and their Developer Docs will help you get started writing your first GTK4 application in Vala really quickly. From there on, you can use the excellent valadoc.org for API reference, or browse the source code of Elementary apps on Github.
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.