MacOS
Throughout the early 1990s, Apple had tried to create a "next-generation" OS to replace its classic Mac OS. The current macOS is a UNIX operating system built on technology that had been developed at NeXT from the 1980s until Apple purchased the company in early 1997. That company was also founded by Steve Jobs following his departure from Apple in 1985. There, the Unix-like NeXTSTEP operating system was developed, and then launched in 1989 (the "classic" Mac OS is much older, as it came out in 1984). The kernel of NeXTSTEP is based upon the Mach kernel, which was originally developed at Carnegie Mellon University, with additional kernel layers and low-level user space code from parts of Berkeley Software Distribution (BSD). Its graphical user interface was built on top of an object-oriented GUI toolkit using the  programming language.