Ah, early GUIs. For comparison, take a look at Xerox' Cedar and Smalltalk, or Wirth's Lillith and Oberon, all from pretty much the same era.
The Lilith systems are often overlooked. They predate the Blit, are programmed in Modula-2, translated to bytecode. Oberon is a bit more well-known, but still not as much as both the language and the OS deserve.
Which in turn took quite some influence from Cedar/Mesa at Xerox. But one might as well say that KDE 4.9 (2012) is based on MacOS (1984), that doesn't make it an "early GUI" in my eyes.
The point being that this is an editable document serving as a user interface. Which, if I remember correctly, some people once envisioned for the web (cf. Amaya[1]), but never really took hold.
The Lilith systems are often overlooked. They predate the Blit, are programmed in Modula-2, translated to bytecode. Oberon is a bit more well-known, but still not as much as both the language and the OS deserve.
Lilith demo video: http://www.youtube.com/watch?v=ob0lznzkykc
Some screenshots & pics: http://pascal.hansotten.com/index.php?page=photos-of-lilith
Cedar demo: http://www.youtube.com/watch?v=0-_zVkrWCOk
(Smalltalk and Oberon are a bit easier to find and more well-known anyway)