You're making the point here. It's the software that makes our lives significantly better, which is the most important one. However, as software is everywhere,

You're making the point here. It's the software that makes our lives significantly better, which is the most important one. However, as software is everywhere, the original question is the same thing as "what physical invention" is the most important one? From one standpoint this could be something like the wheel or electrical light, i.e. Bios, compiler or a network stack in the software world. Or, something way more personal, like health care related software for the loved ones or some more profane stuff. To make the question even less tangible, software in general can be replaced more easily than physical things, most of the time.