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Apple iPod.
It was not the first mobile music player. However, it's capacity was what it set it apart from music players of the time. -
Facebook was created. Again, it was not the first social media service. I cannot think of a single person in my immediate circle (family and friends) who do not have a Facebook account. -
Creation of YouTube. Introduction of free internet videos for everyone. -
Introduction of the Nintendo Wii. Set a sort of precedent for motion tracking type technology. Xbox and Playstation both fought to try and kill the Wii using their own technologies. (Personal opinion): I feel like the Wii sort of softened up the market and was the first widely used consumer level item that slowly got consumers prepared for VR. -
The first iPhone was released. Changed the markets that it was introduced in. Also introduced easily accessible apps soon after.