For a long time, Q4OS has tried to keep the spirit of the old-school KDE 3.5 desktop environment series alive by shipping with the awesome Trinity Desktop Environment (TDE) by default. But the current stable series, Q4OS 3.x “Centaurus”, also includes the more modern KDE Plasma 5 desktop environment alongside TDE to give users more options for tailoring their PCs to their needs. Based on the upcoming Debian GNU/Linux 11 “Bullseye” operating system series, Q4OS 4.0 “Gemini” is now in development and uses the KDE Plasma 5.14.5 desktop environment by default. Therefore, it is using software packages from the Debian Testing repositories.