If you use Linux and want to either read an old Hypercard stack or (possibly to access an old hypercard stack) decompress a stuffit file (extension of .sit) you’re in luck.
I had to do both and found that to read old Hypercard stacks on Linux you can use Dreamcard Player. It’s a slick application that ran without a problem without having to do anything special.
To decompress stuffit files, you can use Stuffit for Linux. It’s a commercial product, but you get a free 15-day trial to do the decompression. From then on, you can either buy it, or ask your Mac-using friends to zip it. (The file I mean…)