Rhapsody

Rhapsody was the code name for an operating system based on OpenStep, that eventually evolved into Mac OS X.

Rhapsody was released in Developer Previews, and was designed around the concept of "boxes" -- a "blue" box to emulate the classic Mac OS, and a portable "yellow" box based on OpenStep (with an embedded Java Virtual Machine), runnable on PowerPC and Intel hardware, under Rhapsody, Windows NT and Linux, and a "red' box to emulate Windows which was never actively developed.

The "yellow" box eventually became forked into the Aqua environment we know in OS X and iOS and GNUStep for Linux and Windows. The two environments only have superficial compatibility today.