Advanced Mac Substitute: API-level reimplementation of classic Mac OS

Advanced Mac Substitute is an API-level reimplementation of classic Mac OS. Unlike traditional emulators, Advanced Mac Substitute doesn’t emulate the hardware on which an operating system runs (except for the 680×0 processor), but actually replaces the OS — so it launches directly into an application, without a startup phase. Advanced Mac Substitute is a factored application. Advanced Mac Substitute is capable of running several applications written for the original Macintosh computer. If you’re feeling adventurous, you can try out Advanced Mac Substitute on Mac OS X (versions from 10.4 through 10.12, at least) or Linux framebuffer.

Source: www.v68k.org