Back in 1994, Apple released the Macintosh Application Environment for UNIX. And it was kind of amazing.
Read the full article (with links to documentation and screenshots) at The Lunduke Journal: https://lunduke.locals.com/post/4812552/remember-when-apple-built-a-mac-os-running-on-top-of-solaris-and-hp-ux-seriously-it-happened
And watch the video version here: https://lunduke.locals.com/post/4843383/when-apple-built-macos-for-solaris-and-hp-ux-in-1994
When Apple built MacOS... for Solaris and HP-UX. In 1994.