Which operating system was developed by Apple in the early 2000s?

The operating system developed by Apple in the early 2000s is macOS. Initially released in 2001, macOS was designed to provide a modern and UNIX-based operating environment for Macintosh computers. It was a significant advancement over the classic Mac OS, incorporating features like a more intuitive graphical user interface and enhanced capabilities for networking and hardware management.

macOS also integrated advanced features such as multitasking and support for modern hardware, which aligned it with contemporary software requirements of the time. This operating system laid the foundation for Apple's continued development of Mac software, leading to subsequent updates and versions that have modernized and refined the user experience.

In contrast, Linux is an open-source operating system that has been developed by various contributors since the early 1990s, and Windows is a product of Microsoft, with its long history predating macOS. OS/2 is an operating system created around the same time as early versions of Windows by IBM and Microsoft, but it is not an Apple product.