Prime95 - Prime95 is a program that searches for new Mersenne prime numbers.
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
System Stability Tester - System Stability Tester - Test your system's stability and performance by calculating millions of digits of Pi.
Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.