Javascript emulator lets you run Mac OS 8 as an app on your Mac.

Hey, you Mac old timers (like me). How many times have you said to yourself, “Man, I could use a round of Duke Nukem 3D right now!” or wished you could go back to a version of Adobe Photoshop that didn’t have all the tools you need? (Okay, never, but play along with me here.)

Well, now you can go back to the old days of the Mac with a Mac OS 8 emulator, written by Felix Rieseberg. He created a JavaScript app which includes a virtual machine that emulates a Macintosh Quadra 900 running Mac OS 8.1. The 261MB compressed download expands into an app that runs that system in a window on your modern Mac.
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https://www.macworld.com/article/3568496/want-to-run-mac-os-8-on-your-mac-now-you-can.html