-
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 a PDF, not sure. But you can clone the repo. There may also be build artifacts you can download, perhaps. But this will probably just get you an HTML format copy, not PDF. I'm not familiar with the tools they use to build the docs, but it may be modifiable to produce PDF output instead of HTML or you might be able to use a tool like pandoc to convert it.
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.