collectd
A daemon that collects system performance statistics periodically, and provides tons of plugins to store and analyze these values
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Errbit
An open source, self-hosted error catching tool, which can collect and manage errors from other applications. It is compatible with the Airbrake API and can be used as a drop-in replacement.
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FastForward
Flexible operating-system event and metric forwarding agent. Receives input and forwards output using plugins.
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FnordMetric
A HTML5/Javascript API for collecting and visualizing time series data
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Instrumental
Instrumental is a real-time, high-scale application and server monitoring tool with intelligent alerts, a powerful query language, and free development accounts.
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jmxtrans
Plugs Java VM statistics via JMX to various backend monitoring tools
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Logstash
A modern tool for managing events and logs, with an ElasticSearch backend which allows a high degree of searching and filtering. It includes a shipper in remote systems, indexer in the aggregator machine, and a Web UI.
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Metrics
Captures JVM and application-level metrics for Java
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Monigusto
A collection of Chef recipes to install various monitoring tools (such as sensu, statsd, etc). Makes it a breeze to get a monitoring infrastructure up and running
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Monit
An open source utility for managing and monitoring processes, programs, files, directories and filesystems
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Puppet Dashboard
A web interface for Puppet. It can view and analyze Puppet reports, assign Puppet classes and parameters to nodes, view inventory data and backed-up file contents, etc.
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Sentry
Automate error tracking to find and fix issues before your users even experience a crash. Sentry is open-source, real-time, and loved by 100,000 developers around the world.
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testssl.sh
A command-line tool which checks a server's service on any port for the support of TLS/SSL ciphers, protocols as well as some cryptographic flaws. It's designed to provide clear output for your "is this good or bad" decision.
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Zabbix
An open source, enterprise-class monitoring framework
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