GEOS was when I went from printing out the terrible line-by-line documents on a $200 Okidata dot matrix printer to printing out whatever fonts could be displayed on the screen. GEOS rendered the entire document (fonts, etc) like a graphics image and spooled it out to the printer. This was the cutting edge of things until the mid-1990s when laser and inkjet printers became affordable.

It sucks there's no good examples on the Internet of what GEOS was capable of, all I see is screenshots, but it was definitely revolutionary for its time.

Interestingly The Newsroom provided some of the same document capabilities a year before GEOS, but I guess they didn't see the broader potential for document design. The Newsroom just did newsletters, but it was a fantastic program and made great use of a large clip art stock.