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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.
As u/Marble_Wraith mentioned. You will find more help and information at r/webdev. That being said, building a Forum is somewhat complex, if you're planning to do so from scratch without any prior knowledge this could be a challenging first task. If it's also an option to use a pre-build app, then https://mybb.com/ is a good starting point. You can also find some information on YouTube about how to get it running.
NOTE:
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Hence, a higher number means a more popular project.