Man's greatest invention

Weird thought bouncing around in my head today. I keep coming back to asking myself what I would consider to be man's greatest invention. Not an easy one. For one thing, "greatest" needs to be defined: does it mean the most important in terms of use, impact on the human race, universality, etc. It's probably a mix of all of these and others I haven't thought of yet.

So, considering this, what great inventions come to mind? Certainly the wheel is important, it is still used everywhere using more or less the same basic architecture as in its very beginning. Writing is another key one; it certainly developed independently in many societies, showing that it is an essential part of our humanity. If we go back further, we could say speech and vocabulary; after all we couldn't communicate otherwise. All these are great in their own right and I am sure we could think of hundreds more to add. That being said, I think Man's greatest invention, in terms of universality, impact and usage must be the concept of God. Every society, ethnic group, tribe I know of has gods of some form or another. These gods serves many purposes: blamed for misfortunes, praised for good fortunes, begged for mercy or victory, etc. The concept of god has help many generations of human beings navigate through life's events, confront its trials and tribulations, in a word, make sense of their existence. As inventions go, it's a pretty good one. I wish I had a patent on that concept! Imagine the riches!

So, if at a certain level the concept of god is a valued invention, it looses it value when it becomes a cause for war, a way to justify ignorance, a means to segregate people. Gods were invented to help people in their daily lives, not to take those lives away or make them miserable. We should go back to the true reason why gods were created and find some common ground between all religions, accepting that none of them have exclusive rights on the truth.