InfluxData - Scalable datastore for metrics, events, and real-time analytics.
Tile38 - Geospatial database and real-time geofence server for managing fleets, mobile apps, and IoT devices.
TimescaleDB - TimescaleDB is a time-series SQL database providing fast analytics, scalability, with automated data management on a proven storage engine.
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.
VoltDB - In-memory relational DBMS capable of supporting millions of database operations per second