TECO
From Just Solve the File Format Problem
TECO (Text Editor & Corrector, or originally Tape Editor & Corrector) is an early text editor (originally implemented on DEC mainframes and minis) which was also a programming language, of the sort in which every character is a command. Programs in it were said to resemble line noise. EMACS was originally written in TECO (as a set of "Editing Macros").
