Long before HTML conquered the world Apple released a hypertext system in 1987 named HyperCard. It was used for many purposes, even games and as a presentation software.
Originally it was created by Bill Atkinson and given to Apple under the condition that it must be made available for free on all Macs.
Later version 2 was released in 1990, HyperCard 3 was shown to the public in 1996 in an alpha-quality version on the Worldwide Developers Conference. Finally Apple stopped selling the system in 2004.
Now you can download a free grammar for Synalyze It! and Hexinator that decodes most of the HyperCard stack files. The file format can be easily displayed in a tree view.