System

KShutdown – free and open source, multiplatform graphical utility for shutdown computer

ClamTk – frontend for ClamAV for the free and open source ClamAV antivirus, simple and light-weight, on-demand virus scanner for Linux

Brightness Controller – free and open source, simple utility to control brightness, RGB, and color temperature of displays in Linux

Y PPA Manager – free and open source graphical software for managing PPA repositories

Etcher – free and open source, cross platform and simple software for safe image writing to SD cards and USB drives

KDE Connect – software for connecting and syncing a computer with the KDE (and others) graphics environment and an Android smartphone

K4DirStat – free and open source, a small utility that visually displays the disk space used for Linux