This is a fascinating bit of history. Start with this Twitter thread by Steve Troughton-Smith:
Neat: there was a licensed Macintosh ROM kit for NeXT machines—effectively let them boot Mac OS as the 1st Mac clone https://t.co/no91kOxhmM
— Steve T-S (@stroughtonsmith) February 11, 2017
Here’s a video showing the Daydream ROM Box at work. Nice find, Steve.
UPDATE: Loop emeritus Peter Cohen brought up the Outbound laptop and the fact that it deserved consideration as the first Mac clone. Fair point. Though the Outbound required you to bring your own ROM, which (at the time) meant removing the ROM from an existing and expensive Mac. I’d argue that the Outbound was more of a repurposing of an existing Mac, rather than a clone, but interesting nonetheless.