What operating system was developed by IBM and Microsoft?

The operating system developed by IBM and Microsoft is OS/2. This operating system was a joint project between the two companies during the 1980s and was designed to be a powerful, multitasking environment that could take advantage of the capabilities of the hardware being developed at that time. OS/2 was intended to be an advanced alternative to MS-DOS and provided a graphical user interface alongside multi-user support. Over time, its development evolved, and while it did not achieve the same level of mainstream success as some of its competitors, it laid the groundwork for future operating system advancements and concepts that would influence later systems, including Windows.

In contrast, Linux is an open-source operating system that was developed independently by Linus Torvalds, while Windows is a product of Microsoft but not developed in collaboration with IBM. Mac OS is developed by Apple and has no connection to the collaboration between IBM and Microsoft.