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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.
see also a tutorial on writing a doom-compatible engine from scratch:
https://github.com/amroibrahim/DIYDoom
they also have a community forum, diyidtech, at https://discord.gg/a8n4Y2z
A few years ago I wrote to the author to express gratitude for them writing this book (I also purchased a hard copy to express an additional $0.77 worth of gratitude). One thing I notice hasn't been mentioned yet which is cool is that the entire source code for the book is on GitHub: https://github.com/fabiensanglard/gebbdoom
NOTE:
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Hence, a higher number means a more popular project.