QED is a line-oriented computer text editor.
Originally written by Butler Lampson and Peter Deutsch for the SDS 940, probably in 1966. Ken Thompson later wrote a version for CTSS; this version was notable for introducing regular expressions. QED influenced the classic UNIX text editor ed and the less well known sam by Rob Pike. A Canadian version of QED named FRED (Friendly Editor) was written at the University of Waterloo for Honeywell GCOS systems by Peter Fraser.
See also: QED for other uses of "QED".