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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.
Also, I have pointed others to the open source Xmind: https://github.com/xmindltd/xmind
Have you looked at Minder? I don't know if it will fill all your needs, but it might. You could see if it's in your distro's repositories and give it a try, see if it will do what you want.
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.