Mac OS 9
I'm the creator of the site, thanks for the submission.This is an in-progress port of the SheepShaver emulator to WebAssembly/Emscripten, https://github.com/mihaip/infinite-mac/issues/34 is tracking the remaining work.If you're interested in running older Mac software in the browser, the BasiliskII-based sites at https://system7.app/ and https://macos8.app/ may be better bets. They will boot faster and have fewer compatibility issues (especially System 7).The main thing that Mac OS 9/SheepShaver brings is PowerPC support. There is also a variant of System 7 for PowerPC with more esoteric mid-90s Apple projects like OpenDoc and QuickDraw GX installed available at https://system7.app/?domain=system7-ppc.app.