Back in the early 1970s Xerox PARC created a WYSIWYG text editor called Bravo. It ran on the Alto which had a maximum of 128K of memory. Approximately 3/4 of that memory was consumed just to store the bitmapped screen, so Bravo would have had to run in about 32K.
As a side note, Charles Simonyi (of Microsoft Office fame) worked for PARC at the time. I might be misremembering, but I think he had some involvement in Bravo.