OpenTSDB - OpenTSDB is a distributed, scalable Time Series Database (TSDB) written on top of HBase.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Tile38 - Geospatial database and real-time geofence server for managing fleets, mobile apps, and IoT devices.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
BuntDB - A fast, embeddable, in-memory key/value database for Go with custom indexing and geospatial support
Prometheus - An open-source systems monitoring and alerting toolkit.