KDE vs. GNOME

What are KDE and Gnome?

What they are is desktop environments. That's to say, they define the software environment where the window manager and the other GUI programs run. Gnome (I know zilch about KDE) provides standardized interface components (a bit like Motif did), and standardized preferences. It also provides an implementation of CORBA, for inter object communication. One useful user-level Gnome feature is the ability to save a whole session, so that when you log in again the same programs reopen, and actually open those files you were editing.

For example, I run Window Maker under Gnome, because I like the Gnome taskbar. But I could be running it under plain X.
There are programs, like grip, that require Gnome. Luckily, old "plain-X" programs like xbiff, xterm or xv don't give a damn about the presence of Gnome, and just run happily in their old unadorned way. There exist Gnome-aware subsitutes, like the Gnome terminal.
Some programs require that you have installed the Gnome libraries, but you don't need to be actually running a Gnome based window manager. If memory does not fail me, Galeon works like that.

Many people, especially KDE fans who exhibit the fold-and-merge attitude, think that GNOME is a bad KDE clone. Usually, people don't even know what the differences between both of the projects are.

This is written mainly from a GNOME point of view since I'm a member of the GNOME project. If you want anything added here that doesn't justify having its own writeup, /msg me and I'll add stuff to the list.

• GNOME's GUI toolkit, GTK+, is based on C and a simple run-time implementation of objects and classes, unlike Qt which is programmed in C++ with some additional keywords that are interpreted by the Meta Object Compiler, moc.
• GNOME hasn't got an own, official window manager, to the contrary: window manager independence has always been an important goal. KDE, on the other hand, was originally supposed to work with KWM and only KWM. Today, however, both GNOME and KDE are supported by about a half-dozen window managers each, and there is a semi-official GNOME window manager (Sawfish)
• GNOME's panel has always had panel applets. KDE's features applets only since version 2.0, which means that the GNOME applet culture has brought forth many more applets to date.
• GNOME's file manager, Nautilus, contains many clever hacks not found in Konqueror (and vice versa, I suppose?)
• GNOME has had widget themes for years, KDE has started supporting them with version 2.0.

This writeup was renoded after being nuked from its original node; the responsible god offered me to put it here, so I did.