So as someone who doesn't have a good grasp on copyright law, I'm not sure how 1984 is on this list. All the other books here appear to be over a hundred years old, making them public domain (I think), but 1984 was published in 1949. Pretty cool site, anyway.
George Orwell died in 1950, so it looks as though that book is already out of copyright in Australia and Canada, for example, but will remain in copyright till 2044 in the USA, while it comes out of copyright at the end of 2020 in the European Union. (But please don't rely on my interpretation of a Wikipedia page if it's important to you!)