TECO
From Computer History Wiki
TECO is a text editor. First written for a PDP-1 at MIT's Research Laboratory of Electronics. Then ported to the Project MAC PDP-6, and for a long time the primary editor in ITS. EMACS was implemented using TECO's programming facilities.
The standalone PDP-6 version was modified by Bob Clements, while installing the SAIL PDP-6, to run on the DEC Monitor. This evolved into DEC's "Standard TECO".