1987: OS/2 - History of Desktop OSs
OS/2, which was possibly the greatest commercial software competition Windows ever faced for traditional desktop and laptop computers, makes a first showing in 1987. Originally developed since 1985 in a joint project between Microsoft and IBM under the code-name CP/DOS, OS/2 1.0 was released without a GUI in December 1987.
The development efforts between the two companies separated in 1990, when Microsoft wanted an open operating system for general PC platforms, while IBM wanted to retain it for its own hardware. The two companies agreed that IBM would maintain OS/2 1.0 and develop OS/2 2.0, and Microsoft would develop OS/2 3.0, but Microsoft decided to rebrand that operating system to Windows NT.
The coexistence of the two operating systems caused significant confusion in the market which of the two operating systems actually was Windows. IBM later released OS/2 2.0 as a 32-bit OS in 1992, branded version 3.0 as OS/2 Warp in 1996, and ceased distribution of the OS in 2005.