Compiz or the many names it was called, Beryl, Compiz Fusion are Desktop Effects, sometimes useless but there were useful ones also. Other plugins added eye candy to the desktop. To this date it beats out any other effects on any distro period.
KDE Plasma Workspaces, KDE Plasma 4 and KDE Plasma 5, provide the environment for running and managing applications. KDE Plasma 4 is the umbrella term for the fourth generation graphical environments. Its successor, KDE Plasma 5 is a set of graphical shells released on July 15, 2014. They include many components such as KWin, KDM, Plasma core libraries, Klipper, KSysguard, and System Settings. There are different available GUI environments: Plasma Desktop for desktop computers, Plasma Netbook for netbooks, and "Plasma Active" for smartphones and tablets.
Want to put your system on a diet? use commandline applications or scripts. In most cases the commandline is just quicker and can be automated to do repetitive tasks. There are way commandline applications to replace just about any GUI apps
Ncurses applications are text interface in the command line, these are nice since they have simple interface but are lightweight and uses very little resource that even crappy computer can feel like a powerhouse.