GoldEd (GED) for the Amiga back in... probably 1992 or 93. Although the Amiga already had good text editors (CED to name one), GED had syntax highlighting and I seem to recall also macros and keyword searching in sources and AmigaGuide docs (think HTML years before the WWW). Back then I was learning the AmigaE language (another gem of that time) and GED turned out quite useful when compiling or simply navigating code.
