Answer: OS/2

In April of 1987, IBM and Microsoft held a joint press conference to announce an ambitious new project, a next-generation operating system dubbed OS/2. The promise was of a faster, better, replacement for MS-DOS that would improve the entire computing experience.

The two companies had been collaborating on the project for the prior two years, although at the time of the announcement, it was still under heavy development—the press conference marked the first of many promises-before-delivery moments in the development of OS/2. Each edition of OS/2 became progressively more delayed (the version released in December of that year didn’t even have a GUI) and ultimately, in 1990, the relationship between Microsoft and IBM unraveled. Windows 3.0 was enjoying sweeping success, carrying MS-DOS right along with it, while OS/2 suffered from stagnant sales and poor driver support.

Although OS/2 did have several clear advantages over MS-DOS and Windows—it was excellent at multi-tasking—it was ultimately mired down in hardware dependencies, poor adoption rates, and an increasingly Windows-centric PC market.

While IBM attempted to re-invent OS/2 several times over the next decade, it ultimately faded into obscurity. The last major release was in 2001 and support was discontinued in 2006. OS/2 hangs on in a few small niche markets, like bank networks and subway control systems, but otherwise exists largely as a footnote in the history of computing.