Classic Mac OS

Basilisk Unity Mode lets you share classic Mac windows within macOS.

On the “spatial finder”, what makes the finder UI on pre-OSX systems a kind of place you can hang out in.

Portal is an early experiment in hypertext/interactive fiction that acts as a boot ROM. The UI replicates Classic Mac OS with some modern features. A space explorer returns to earth after a 100 year journey to find it abandoned, you piece together what happened by reading scraps of documents.