The wheel.

Good question. I wish I had an answer, but I don't. I will say that the one that has had the most profound and all encompassing effect on the development of civilization is written language. I'd say it was foundational.

That is an interesting question that I had not thought of until now. I would have to say that the greatest invention ever is the camera and how that morphed into video recordings. Not only do these things further our understanding of history but as a person that has researched the ancestry of over 50+ families - pictures bring it home. It's one thing to visit a cemetery for names and dates - it's quite another to have pictures of these people and how they lived and labored for us over 160+ years ago.

The boat! But then I'm biased.

Wow, that's a good question, I need to think about it.

Yes, after reading some posts, I'm going with language and writing.

You mean apart from The Wheel, Electricity an the Internet? My "silly answer" is my MP3 player. If you had told me when I was young that you wound be able to fit all my 300 records (both sides) on something as small as a matchbox AND listen to them. I would have thought you were insane in the membrane. BIg Brighton Love Andy x

Transistor

Think the pencil is a brilliant design that is pretty much unchanged since it was created. Simple, functional... the other greatest invention is paper. Then there are books...

I love technologies but most will not function with out electricity. And that can be limiting. When you have a pencil, paper, and imagination the possibilities are endless.

I would go for language. Though whether that counts as an invention or part of the natural course of evolution, I am not certain. Certainly a thought-provoking question!

Silicon chip

Language. It led to other developments.

The printing press

Gas powered ice auger, you would think so also if you ever used the manual labor ice auger.

writing

Symbolic representation of sound, ie... letters

I'd vote for the ability to make fire, when and where it was needed; then there's flint knapping, the beginnings of Science, investigating the 'grain in the stone.'

Alternating Current- Electricity it lights the world and allows a much greater life!

Zero. The concept of nothing is needed to make sense of anything.

Birth control.

The bicameral mind