Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Like enterprise Linux, OS/2 - which celebrated its 25th birthday this week - is one of those operating systems that had "wide adoption," but not outside the realm of IT. But if you've used an ATM sometime over the past 20 years, you've likely used an OS/2 device. Granted, that's kind of like saying you're an Android user if you own an Amazon Kindle Fire: the OS is so buried under layers of security and user interface that you'd never notice the operating system.
OS/2 started as a joint venture between IBM (creators of the IBM PC) and Microsoft (oh, you know who they are) in 1985, with OS/2 1.0 shipping in April 1987. It had the backing of the then-largest maker of PCs, but it ultimately failed since the only way to get OS/2 pre-installed on a PC at the beginning was to buy a PS/2 from IBM.