I remember SQLWindows of Gupta Technologies (later renamed to Team Developer of Centura Technologies IIRC) which had an outline IDE. Quoting from https://yagnipedia.com/wiki/sqlwindows :

SQLWindows had an outline-based code structure — not braces, not BEGIN/END, but an indented tree that was simultaneously the code and the IDE’s display. You wrote code by expanding and collapsing outline nodes. Classes were outline headings. Methods were sub-headings. Code lines were leaf nodes. The entire program was a hierarchical outline that the IDE rendered as a collapsible tree.