The Kaladesh Inventions are a set of reprinted cards in a premium foil design which are inserted into the sets Kaladesh and Aether Revolt. All of them are popular artifacts from Magic's history with a new artwork and a special border, fitting the theme of the Kaladesh block. They are similarly rare as foil mythic rares, and will only exist in English. If you open a German or Japanese Kaladesh pack, you can still find an Invention, but it will be in English independent of the language of the rest of the pack. Opening one of these beautiful cards should be really exciting! These cards are legal in Limited, but only legal in the constructed formats they already were legal in before the reprint.
In the future, every block will come with such a premium set of reprint cards, chosen to fit the theme of the block. The general term for all those reprint sets is “Masterpiece Series”, but each of them will have their own name as well.