Better than the rest
OS/2 did a better job of being a single-user, multitasking, operating system than any of the current ones. It also ran on hardware comparable to a simple cell phone. A superb tecnical achievement!
In addition, it later got a GUI that is far, far superior in design to what Microsoft has today.
And therein lies the problem: IBM and Microsoft co-own the (c) to the code (some of it is even owned exclusivelly by MS). Don't expect this to ever become public domain (less MS goes belly-up).