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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.
Here https://github.com/ethereum/go-ethereum , or if you don't want to host it yourself: https://infura.io/ .. both are free
Unlike Infura the code they run their system on is open source so you can run it yourself if you want to.
They also have a project called plugeth—which is a Geth fork that integrates the Golang plugin framework.
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.