I've been "maintaining" this collection of stacks for around three years - keeping the uploader[2] running (yes, you can add your own stacks!), checking the stacks for bugs / errors in the emulation, etc... and the range and breadth of what was created in HyperCard is just amazing.
You've got silly little animations[3], sound samplers[4], choose-your-own adventure stories[5], reference guides[6] and teaching materials[7] (that last one was added to the collection with the very kind help of someone at the USGS who mailed me a CD-ROM so I could add it).
I thoroughly recommend that those unfamiliar with HyperCard have a browse of the collection and see what was made possible by this groundbreaking 1980s tool.
[1] https://archive.org/details/hypercardstacks
[2] http://hypercardonline.tk/
[3] https://archive.org/details/hypercard_computer_sind_doof
[4] https://archive.org/details/hypercard_cheapsequencersit
[5] https://archive.org/details/hypercard_inigo_gets_out
[6] https://archive.org/details/hypercard_macprinters-11
[7] https://archive.org/details/hypercard_usgs---teaching-earth-...