Nagios is a host, service, and network monitoring system that will watch your network and alert you to problems before your clients or end-users do. The system runs checks on hosts and services that you specify using plugins that return status information to Nagios. When problems are encountered, the system will send notifications to system administrators so that they can take action on the problem. The JumpBox for Nagios gives you a head start to using the system. It eliminates the complexity involved in getting the application installed, and allows you to focus on the configuration for your specific environment. Since Nagios is based on plugins, depending on what you want to do this will vary in complexity.
mod_top is a production monitoring tool for LAMP applications with user interfaces modeled after the popular Unix top. It plans to support PHP, Perl, Ruby, Python, mySQL, PostgreSQL, and Apache 1 and 2 on Linux. It can help you locate bottlenecks in applications, troubleshoot high memory consumption, understand CPU utilization under load, diagnose causes of slowness or heavy resource utilization, or discover database dependencies.
Ultimate Boot CD is a collection of Freeware and Free Software tools for PC diagnostics and maintenance. Included are tools for BIOS editing, CPU and memory testing, boot management, data recovery, peripheral and system inventory, and hard drive partitioning, cloning, wiping, diagnostics, and low-level editing. All tools boot and run from the CD.