We’ve seen a System 7 Mac emulator before, as an app, but a developer has now created a version which runs directly in a web browser …
System 7 was the first classic Mac OS system to be later renamed as Mac OS, with version 7.6 being rebranded as Mac OS 7. That naming scheme later evolved to Mac OS X and then to the macOS we have today.
It was the longest-lived Mac operating system, launching in 1991 and finally replaced by Mac OS 8 in 1997.
System 7 spanned the processor switch from Motorola 68000-series to PowerPC, and while it introduced a lot of welcome new features, the introduction was controversial. It was the first version that could no longer be run on older floppy-disk Macintosh models, and it also used a lot of RAM, causing even some hard drive models to struggle.
Källa: System 7 Mac emulator lets you play with a 1991 Mac on the web