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.
AWS CloudTrail - AWS CloudTrail is a web service that records AWS API calls for your account and delivers log files to you.
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.
Logmatic - Logmatic is a log centralization, analytics & visualization platform to improve software & business performance.
Prometheus - An open-source systems monitoring and alerting toolkit.
log4net - log4net is a tool to help the programmer output log statements to a variety of output targets.