GNOME (GNU Network Object Model Environment) is a desktop environment and graphical user interface (GUI) that runs on Unix-like operating systems. It is composed of free and open-source software and is developed by an international community of volunteers. GNOME provides users with an intuitive and attractive desktop environment, which includes a variety of applications such as a web browser, an office suite, media players, and other utilities. GNOME also includes features such as a panel, a window manager, and a number of customizations and settings. It is designed to be simple to use and able to run on low-end hardware systems. GNOME is the default environment for many popular Linux distributions, such as Ubuntu and Fedora.
KDE makes two desktops that are alternatives to GNOME: KDE 4 and its successor, Plasma 5. Both are popular, extensible and support Qt much more than GTK. KDE is known for having a lot of built-in options (rather than access through extensions, as in GNOME). It is also a more "classic" desktop experience: people coming from Windows will find it more familiar than GNOME.