InfluxData - Scalable datastore for metrics, events, and real-time analytics.
Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
Prometheus - An open-source systems monitoring and alerting toolkit.
Kafka - Apache Kafka is publish-subscribe messaging rethought as a distributed commit log.
VictoriaMetrics - Fast, easy-to-use, and cost-effective time series database
Snare - Snare is well known historically as a leader in the event log space.