The M&R Enterprises Sup'R'Terminal was the first Apple II peripheral card to enable the display of 80 columns of text on a connected monitor.
As the first card making 80 columns of upper and lower case text displayable on these machines, it is the only card supported by the II+ version of Apple Writer and thus the only way to see on a monitor the true layout of text as it will be printed on a page with this popular early personal computer word processor.
This transition to 80-column display was an early step in bringing the WYSIWYG concept to the Apple ecosystem.
A variety of clone add-on cards with similar functionality were released in the wake of the Sup'R'Terminal, including the Videx Videoterm.
[1] The Sup'R'Terminal was designed by John R. Wilbur and the firmware was written by Andy Hertzfeld in 1980.