The artificial satellite used for communications relay, by Isaac Asimov. He also invented what may be interpreted as the internet search engine. 'Multivac' access stations were available to all in several of his stories, to be used in the same way we use Google etc. Multivac being a mega supercomputer.
If you go back far enough you'll find televisions, mobile phones, camera phones, flying cars, VTOL aircraft, the list is endless.
It seems that if a writer can think of something, eventually it will be invented.
One interesting story I remember involved a group of engineers being shown a film of a man using an anti gravity back pack, they were then told a rival country had invented it, could they match it? Well they did, only to find out that the film had been a fake!
Pete