As regular readers know, one of the things I love about Emacs is its recapitulation of the Lisp Machine. Like most developers, I never had the chance to work on a real Lisp Machine so Emacs is as close as I can get. Sometimes, it's easy to imagine that they're the same thing. But they're not, of course.
Take the Emacs documentation system for example. It's truly a wonder—far better than anything other programs offer. Write your own function, add a docstring and your function is automatically added to the documentation. Extraordinarily powerful and wonderfully helpful to the end user, it's hard to imagine how it could be significantly improved.
Hard, that is, until you see how the Lisp Machine did it. I can't begin to describe how extraordinary Concordia—the Lisp Machine documentation system—was. Fortunately, I don't have to. Rainer Joswig has a wonderful video that shows Concordia in action. One of the really nice aspects is how great the authoring system is. The system is object oriented and all changes are effective immediately.
If you like the Lisp Machine aspects of Emacs, you won't want to miss this video. It's just less than 20 minutes long so you won't need to block out a bunch of time.