The Automobile

Though under development in Europe during the nineteenth century, the automobile didn’t really become a practical and reliable source of transportation until the twentieth century. Once it did, it changed everything; overnight the horse and buggy became quaint anachronisms while much of the country was paved over to make room for endless ribbons of asphalt. It also brought about a revolution in the market place, suddenly making it possible to truck in goods that otherwise would be impossible to acquire. Most of all, Henry Ford’s assembly-line production style made the automobile affordable and accessible to the average person (before Ford’s Model T was introduced in 1908, only the fabulously wealthy could afford a car). The automobile gave everyone a degree of mobility and personal freedom our forefathers could only dream of, and turned entire generations of teenagers into raging revheads.
Source:

http://www.toptenz.net/top-10-inventions-of-the-20th-century.php

Apple iPod (2001)

Portable MP3 players had been around for many years before Apple launched its version in 2001, but the iPod – together with Apple's iTunes software – was the technology that really transformed the way people listened to music. The device's large internal storage capacity meant it was no longer necessary to carry around CDs or cassette tapes, and the sleek design made it a desirable item to own.

source: http://www.telegraph.co.uk/technology/picture-galleries/11298840/Most-important-inventions-of-the-21st-Century-in-pictures.html

The Airplane

Just as the locomotive made the world a smaller place in the nineteenth century, the airplane did the same for us in the twentieth century, shrinking our planet to the point that a person could fly anywhere in the world in a matter of hours. Not only have they made travel quick and safe, but aircraft provide many other services as well: from crop dusting and fighting forest fires to overnight delivery of packages and chasing hurricanes. They have also revolutionized warfare, turning battle into a long-range affair fought at arm’s length by machines of such sophistication that the way wars are fought has completely changed. Of course, they’ve also been responsible for leveling whole cities and bringing war to the civilian population—who had rarely been directly affected by war until the twentieth century—but then no invention is perfect.

Source:

http://www.toptenz.net/top-10-inventions-of-the-20th-century.php

Nuclear Power

Nuclear power was to the twentieth century what steam power had been to the nineteenth: a game changer. Suddenly humanity had a power source that didn’t pollute, was efficient and practically unlimited, and so had the potential to change the planet overnight. Unfortunately, it was a two-edged sword in that this same energy source could be used to create the most destructive weapons in history, threatening human survival with its very presence. Additionally, while nuclear power plants didn’t spew pollutants into the air, in the hands of the truly incompetent they had the capacity to render whole regions radioactive and, as such, uninhabitable for generations (as was demonstrated at Chernobyl in 1986).

However, it is hard to deny the overall positive impact nuclear power has had. The fear of mutually assured destruction probably prevented the world from experiencing a third world war and, when operated safely, nuclear power plants truly are a superb and cost-efficient energy source that has the capacity to power entire cities. The only question is whether we’re mature enough to handle that power into the next century.

Source: http://www.toptenz.net/top-10-inventions-of-the-20th-century.php

Personal computer

It’s difficult to imagine our world today without computers. Of course, they have been around since World War Two, but they were clunky, massively expensive things that had all the calculating power of a brick. When Steve Wozniak and Stephen Jobs introduced the Apple in 1976, however, it changed everything and the rest is, as they say, history. Today, of course, they are everywhere and we have become so dependent upon them that many people almost feel naked without one. For some, they even provide the very means of maintaining a livelihood: we use them to keep track of our finances, write books, design logos and sell real estate. Plus, they are rapidly replacing the stereo and television in their ability to entertain us with music, movies, and games. Makes it hard to understand how our ancestors did so well without them, doesn’t it? (Image: the Apple 1, 1976.)

Source:  http://www.toptenz.net/top-10-inventions-of-the-20th-century.php