@ajr One of the big losses of not being able to run #HyperCard is the loss of the ability to run Voyager CD-ROMs. They were associated with the Criterion Collection. Titles includes Art Spiegelman's graphic novel Maus, two volumes of Poetry in Motion, The Residents Freak Show, Laurie Anderson's Puppet Motel, etc.
Article mentioning HyperCard: http://www.inventinginteractive.com/2010/02/22/voyager-1989-2000/
Wikipedia including title list: https://en.wikipedia.org/wiki/Voyager_Company
@ajr Back cover of Poetry In Motion II published by Voyager. Note System Requirements - it ran on Windows too, so maybe this one is not HyperCard based. Video resolution was fairly low - this is a CDROM, not a DVD-ROM!
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@ajr Voyager CDROM catalog. Some titles are Macintosh-only (seemingly earlier, HyperCard based ones before they moved to a multi-OS authoring system, perhaps.) This page about a Voyager CDR that also ran on Windows still mentions HyperCard when it runs on a Mac. http://web.media.mit.edu/~minsky/Voyager.html
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@larrybob I greatly appreciate this wealth of info!