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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.
I think it's a misnomer to say that CTFd is proprietary. While CTFd does have a hosting platform that uses closed source code, CTFd itself is open core and open source under the Apache 2 license. My company and I put a lot of effort into maintaining the open source version of CTFd while still being sustainable.
NOTE:
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Hence, a higher number means a more popular project.