nxlog - NXLog offers log management solutions for companies of all sizes.
logstash - logstash is a tool for managing events and logs.
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.
rsyslog - Rsyslog is an enhanced syslogd supporting, among others, MySQL, PostgreSQL, failover log...
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Splunk - Splunk's operational intelligence platform helps unearth intelligent insights from machine data.