Fluentd - Fluentd is a cross platform open source data collection solution originally developed at Treasure Data.
log4net - log4net is a tool to help the programmer output log statements to a variety of output targets.
logstash - logstash is a tool for managing events and logs.
Serilog - Backend Development and Utilities
Fortinet FortiAnalyzer - Fortinet FortiAnalyzer is a powerful product for Security Fabric Analytics and Automation.
LOGBack - Logging framework