Neofetch - Fancier version of Screenfetch that displays colors and supports more platforms.
CPU Frequency Selector - Cinnamon CPU Frequency Selector Applet
Archey 4 - Archey 4 is a system information tool written in Python
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.
Prime95 - Prime95 is a program that searches for new Mersenne prime numbers.