CPU Frequency Selector - Cinnamon CPU Frequency Selector Applet
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.
Udev Discover - A helping tool for udev testers, coders, hackers and consumers.
Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.
HeavyLoad - The individual test methods employed by HeavyLoad can be customized to fit your needs.
System Stability Tester - System Stability Tester - Test your system's stability and performance by calculating millions of digits of Pi.