Despite its unpronounceable name, Gkrellm is a really handy tool for those who like to keep an eye on resource management.
The program displays a narrow interface where you have a complete system resources analysis at a glance. You'll be able to check CPU usage, memory usage, processor load, incoming and outgoing network connections and other details.
Gkrellm is fully customizable, meaning you can select exactly which specific modules you want the program to monitor. Simply right click on the program's title bar or press F1. You'll be able to choose among several different modules: clock, CPU, memory, file system, battery, uptime and some others.
Apparently the program also supports themes, but there's only one included in the installation – default – and to be honest, it's not very eye-catching.
Gkrellm is a complete system resources monitoring tool with which you can have CPU, memory, network and other key elements under control.