Pierre Lorenzi has built something wonderful:
HyperCardPreview is an Mac OS X application that can display HyperCard stacks, with an look very faithful to the original. It makes the stack files alive again in the Finder with their real icons, so they don’t appear as “binaries”, and provides a QuickLook plug-in.
It can only visualize the stacks: it can’t modify them, and it can’t execute them. But it lets the user inspect the stacks, backgrounds, cards, buttons and fields, see theirs scripts and get their text contents.