PCLinuxOS, originally a fork of Mandrake/Mandriva Linux, was created by some guy known as "Texstar" from a set of RPM repositories for Mandrake 9.2 that he developed.
The default desktop environment is KDE, but these screenshots are of the XFCE "Phoenix" edition.
The PCLOS "Plymouth" boot splash program, which has been customized for the Phoenix edition.
This is the default desktop. That whole metal theme of the boot splash has been carried over into XFCE.
PCLOS Phoenix is based on XFCE4.
Really there is nothing special about it. You have your two standard "panels", with a group of menus, some links, and a notification area, you have a "show desktop" button, some "No data" thing I don’t know what it is, a screenshot button, a desktop switcher, and a trash can icon.
This is the applications menu. Again, it is standard XFCE stuff.