System

Guvcview is a free and open source, simple program for capturing and viewing videos from v4l2 devices for Linux

GSmartControl is a free and open source, multi-platform tool for checking the health of a hard disk and SSD

Redshift Control Plasma – free and open source applet for automatically adjusting color temperature of screen depending on time of day in KDE Plasma

f.lux – free and open source program that adjusts the color temperature of the monitor in accordance with the geographical location and time of day set by the user

Redshift – free and open source program for automatic control of the screen temperature

KRuler – free and open source on-screen ruler for measuring pixels for Linux