The original release of OS/2 did not include a GUI. Version 1.1 was the first to include the "Presentation Manager" GUI, which appears to have been designed by Microsoft and is running on top of IBM's operating system.

In the early days of OS/2 Microsoft and IBM were working together on the project. Microsoft's original intention was to replace Windows 2.x with OS/2. However, after the release of OS/2 1.3 Microsoft and IBM had some sort of quarrel that resulted in the partnership splitting up. IBM took what they did and created OS/2 2.0 and later, while Microsoft took what they had done and worked on their Windows NT, as well as Windows 3.x and later.

This is the OS/2 desktop. It looks pretty much the same visually as Windows 2.0 of the time, except with a different color scheme.

It is iteresting to note that OS/2 1.1 came out in 1988, well before Windows 3.0, and yet here we have what is essentially an early version of the Program Manager being used as a shell. Windows 2.0 was stuck with the old and crappy MS-DOS Executive.
The "Start Programs" thing is not exactly like the program manager however. It is not an MDI application, and therefore it does not use any child windows. It also doesn't use any icons.

OS/2 also got an early version of the File Manager.

OS/2 comes with a pretty extensive help library. Unlike Windows 3.0, there are no clickable links with this help system, even though each file does have an index you can browse.

Note that OS/2 is pretty keyboard-shortcut-intensive. There is a shortcut key for practically every single operation you can perform, and these shortcut key combinations are not hidden from the user.

Oops.

The control panel is pretty much identical to the one in Windows 2.0.

Menus in OS/2 are a little bit on the funky side. There is no exit option under the File menu, rather each program has a separate Exit menu. The Resume option is for exiting menu selection mode while using the keyboard.