As we have seen, Linux systems contain a great variety of tools: tools to help manipulate files, transfer data, compile code and so on, but they also contain tools that let you track and analyze the performance of your PC, by evaluating the way your PC uses hardware and system services, including RAM, CPU and hard drivers. With the information provided by these tools, you can uncover potential problems, locate and fix performance bottlenecks and make sure your computer is running in tip-top shape.

Besides the tools that are included in most Linux distributions, you’ll also find additional ones available on various websites and in your distribution’s repository. Basically, they’re divided into three categories:

• Tools that run in a graphical interface (X11)
• Tools that run in a console (terminal)
• Tools that run on a web server (Apache)

Source : softpedia

X11

• GKrellM

Desktop Included Tools :

• gnome-system-monitor
• KSysGuard
• SuperKaramba

Console based:

• saidar
• htop

Web based:

• phpSysInfo
• DarkStat