-
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 would point to tSIP, although it really depends what other requirements are (for example it does not support video). As most (all?) open source softphones are free it might make sense to test and provide instruction for few different ones, giving the choice for end users.
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.