I'd say Democracy and the Parliamentary system are two of the main
great achievements. But how can these be claimed to be modern
inventions when they have been around since antiquity?
The concept an "engine" -- a machines that consumes fuel and produces
work -- has been around for millennia so how can modern science be
credited for the combustion engine? It is the same thing with the
concept of Democracy. The ancient Greek city states had some form of
Democracy, just like they had engines, but it was flawed and
eventually overrun by usurpators.
During the late Renaissance and Enlightenment philosophers started to
question prevailing forms of government in which one ruler was
supreme. This led to parliaments being formed and power shared between
entities. One prominent example was the 1688 overthrow of the King of
England and the declaration of the supremacy of the English
This led to other parliamentary systems being created, such as the
American one in 1776 which heavily drew upon European enlightenment
philosophy and the lessons of earlier revolutions. I think this period
was the beginning of modern Political science. Not only did
philosophers espouse various maxims about "natural and inalienable
rights", but they also began thinking about how these rights could be
implemented in practice.
In doing so, they had to draw upon lessons on what had worked well in
the past and what had not worked so well. This meant the endeavor
became scientific. For example, the American colonialists borrowed
good ideas from the English Bill of Rights, then the French
revolutionaries borrowed ideas from the American Declaration of
Independence and so on.
Each of these upheavals led (for the most part) to the establishment
of better and better systems. They are more safe from usurpators, more
democratic and more stable than they have been in the past. For
example, Donald Trump is the president of the United States and the
most powerful person on earth but not even he has unlimited power to
do whatever he wants. That this kind of "power sharing" for the most
part works, is a great achievement.