Datadog is a monitoring service for cloud-scale applications, bringing together data from servers, databases, tools, and services to present a unified view of…

Graylog helps you can observe any established or rejected network connection, find those that are unusual to tighten rules and mitigate attacker activity.

Nagios Log Server is centralized log management, monitoring & analysis software. Quickly & easily manage, monitor and analyze log data.

Fluentd is a cross platform open source data collection software.

Logstash is an open source, server-side data processing pipeline that ingests data from a multitude of sources simultaneously, transforms it.

Scalyr is a server log monitoring tool.