-
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 they don't trust F-Droid or something like that? I found this, take of it what you will.
Not sure if this is what you want but Matrix (https://matrix.org/) is also a good choice. It's an open protocol so there are many client applications for it. The most popular one is Element which is available on F-droid: https://f-droid.org/en/packages/im.vector.app/ .
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.