InfluxDB

InfluxDB is a time-series database that records measurements against a timestamp and indexes them by tags, so you can ask what the average value was over a given window. Writes are append-only and land in shards, and the query language is built around time ranges, downsampling, and aggregation over the stored series.

Teams use it for infrastructure and application metrics, IoT telemetry, and monitoring dashboards rather than for transactional workloads.

Running it on your own cluster keeps the full monitoring history private and removes the per-user pricing that comes with a hosted time-series service.