logstash - logstash is a tool for managing events and logs.
Serilog - Backend Development and Utilities
rsyslog - Rsyslog is an enhanced syslogd supporting, among others, MySQL, PostgreSQL, failover log...
log4net - log4net is a tool to help the programmer output log statements to a variety of output targets.
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.
Logary - Professional logging metrics and analytics for your apps