OS/2, which is short for "Operating System/2", is a 32-bit, preemptive multitasking operating system for the 386 and higher x86 processors originally developed as a joint effort between Microsoft and IBM several years ago. Since then, however, IBM and Microsoft have gone their separate ways and IBM is now the sole developer of OS/2.
If you have a 486 or better processor and 6+ megs of RAM (4 would work..), get yourself a copy of OS/2 Warp -- it will be the best thing you ever did. Granted, it may take you a week or so to adjust to the new interface, but in a few weeks you'll be doing things that you never thought possible...both with your old DOS and Windows applications and with new and advanced OS/2 32-bit applications. Oh, and believe me, once you get used to OS/2's multitasking and try to use your friend's Windows system, you'll probably make it do too much and crash it. So be kind to your friend and tell him/her to purchase a copy of OS/2. Any respectible software store should have it.
The "fullpack" version of OS/2 Warp has recently been released and is available in stores. This version comes with it's own, optimized windows code which allows it to run windows applications more efficiently than using the original windows code that may already be installed on your computer. In either case, OS/2 has no problem running Windows applications.
To see an image of the OS/2 Workplace Shell(tm) interface, select this link.