Isn’t fire more of a discovery rather than an invention?
Hot water. I could give up a lot, but I can’t imagine starting my day without a nice hot shower.
I nominate the stick.
Lever,
Poker,
Ball hitter, puck smacker, reacher, hunting device, farm tool. A large stick sliced in a cross section is a wheel, a smaller one is an axle or rollers. Many everyday items come from the stick.
The tractor also deserves a place on this list.
Have you ever watched British Parliment in session? What they are doing is not “collective progress”.
I don’t know if it is a single ‘invention’ but more a series of inventions, but the industrial and agricultural revolutions of the 17th and 18th century led to enough surplus labor that we could devote more labor to science and development, leading to the leapfrogging advances we’ve seen in the last 300 years.
Yes. Unless it is a controlled fire started by humans to cook food and to keep warm, which may have altered the dietary habits and formed groups.
All because of the plow.
Nah, a stick is just a failed boomerang.
I nominate the wedge if you want a simple tool.
Hollow out the stick and you have a pipe.
For irrigation.
And sanitation.
Any chance there’s cave art depicting the first wedgie? 
The first tool must have been a rock.
MASTURBATION
Seriously!
Think about the benefits of ‘going solo’ for a moment.They are numerous; the list below is by no means exhaustive:
-Disease free
-Don’t have to spend lots of time and money
-No ‘hangovers’
-Free from complications that bedevil regular sex such as pregnancy
-No worries about not being satisfied/satisfying the other party
-Get to know yourself better i.e. what your body really responds to
Don’t know whether it can really be classified as an invention but however you classify it, it remains great
I’m sure Jocelyn Elders would back me up on this!
Playstation 3!
Seriously, the greatest ‘invention’ is electricity, due to our dependence on it. When it goes out, we simply stop.
In historical order: language (not just speech but structured and commonly agreed speech), writing, printing, telecoms. Note that that the last includes the internet. Each of those engendered momentous changes in human civilisation.
If you restrict it to physical things, then the wheel is the prime contender.
Which came first, wheel or writing?
I considered this, along with fire, but ultimately see both as ‘discoveries’ instead of ‘inventions’. I can see the argument either way, though.
I suggest reading, since writing wasn’t useful until reading was invented.
Ironclad logic! No way to argue.
Makes one wonder if the first useful book had the title “How To Read.”
Clothing. Nothing else comes close to it’s ability to increase our available territory and therefore the diversity of food, climate, and challenges we can take advantage of.