Windows - IBM OS/2
OS/2, Version 1.0

1985: IBM and Microsoft announced they were working together on future PC operating systems.
Microsoft wanted to use Windows, while Big Blue pushed its own code. The issue was still unresolved when the two companies announced OS/2, Version 1.0 in April 1987.
OS/2 was originally writen for the 286. The 286 had introduced what Intel called "protected" memory and the ability to write programs beyond the 640K barrier, but it did so in a way that sometimes made it incompatible with existing 8088/8086 based software. A "compatibility box" let the users run some existing DOS programs, but early versions of the compatibility box weren't all that compatible; users often called it the "penality box."
IBM and Microsoft started divorce proceedings shortly after Windows 3.0 (1990) came out. IBM took OS/2 2.0 back from Microsoft and started working on adapting it to run Windows apps. Big Blue eventually succeeded well enough that developers had less incentive than ever to write native OS/2 programs.
Microsoft kept its 386 only successor, OS/2 3.0, which became Windows NT.
This image was taken from an OS/2 WARP demo program from IBM
If you want the demo program click on the image to download the zipped file (1.2meg)
Click me to download the program!

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