I came across a web page a few years ago that talked about the unrealized promises of X Windows. Ten+ years ago, X programs looked like crap because there weren't any good (open) X toolkits that were easy to code to. As a result, there were all sorts of experimental prototypes like xedit, xrn, xman and the like.
The guy being interviewed (or the guy who wrote the page, I forget) talked about how the idea of window classes in X was set up so that you wouldn't have to roll your own text editor each time you needed to bring up an editing window -- you should just bring the user's preferred editor in a new window your application creates. (This is the behavior people expect in a terminal window when applications respect the $EDITOR environment variable.)
Alas, no one figured out that was what X apps were supposed to be doing. But the idea wasn't forgotten. Now there's KVim, VIM integrated into KDE as a KPart. The screenshots show that the idea wasn't forgotten, and is indeed alive and well.
