OS/2 was developed as a joint venture, under the codename "CP/DOS" initially, between Microsoft and IBM in the late 1980s through to 1990 when the agreement fell apart. Microsoft's original intention was to replace Windows with OS/2, but when that didn't work out, they took what they had developed and produced Windows NT while developing the existing Windows product into Windows 3.x. Meanwhile, IBM took what they did and produced OS/2 2.x and later, long before Windows NT.

This is the first version, released in April 1987. It doesn't technically fit into a site known as "GUI Central" since it doesn't actually have a GUI at all, but I am including it purely for historical preservation's sake. Plus, it's interesting to see where operating systems get their roots from.

These screenshots were made possible using the PCem emulator, emulating a generic AMI 286 system with CGA graphics. Because of the way the CGA emulation is done, these screenshots may look a little weird.
Note that if you wish to run the same emulator, you will need to obtain the AMI BIOS dump. I don't know how legal it is to distribute it so I won't, but it is freely available online if you search. The file you need is named "amic206.bin". Anything else won't work, and I don't know if renaming a file is sufficient enough to trick it into working.

The OS/2 1.0 splash screen.

This is what you get when you boot up OS/2 1.0. The Selector as it is called is really nothing more than what Power Menu for DOS is, or something like a modern boot manager. It seems to be mostly keyboard-oriented, and even though there is mouse support I couldn't get it to work with a mouse.

Adding programs appears to be done completely manually.

Some of the included help files with OS/2 1.0.