Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
rsyslog - Rsyslog is an enhanced syslogd supporting, among others, MySQL, PostgreSQL, failover log...
Kafka - Apache Kafka is publish-subscribe messaging rethought as a distributed commit log.
Fluentd - Fluentd is a cross platform open source data collection solution originally developed at Treasure Data.
Snare - Snare is well known historically as a leader in the event log space.
logstash - logstash is a tool for managing events and logs.