Stars
Logstash - transport and process your logs, events, or other data
Search Web Application for hard drive documents
Kibana was acquired by Elastic in 2013. See elastic/kibana. More info at http://kibana.org
Fluentd: Unified Logging Layer (project under CNCF)
Graylog Extended Log Format (GELF) implementation in Java and log4j appender without any dependencies.