Regarding the third-party applications and plug-ins for Nagios, there is the Nagios Exchange portal that categorises extensions across various genres.
Both community and commercial support is available for Nagios.
Hyperic is an open source network management suite that targets itself as being suitable for Web application and virtual machine management.
The commercial Hyperic was acquired by SpringSource, which was then acquired by VMWare.
Hyperic features automatic discovery and records some 50,000 metrics across 75 application stacks.
An Enterprise edition is available for Hyperic which includes more features than the open source edition and commercial support.
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