freeShop is a homebrew that makes easy to download games that you already own from Nintendo's servers, in an open-source way.
However, that said titles are stored in a file called encTitleKeys. This file is illegal to share and contains all user purchased titles. And here comes to play an homebrew called freeShop launcher. At start, that homebrew downloads the latest title keys from here and then starts freeShop, allowing a download of all available -and not- titles on the eShop, even titles of the “Nintendo Ambassadors Program”.
freeShop makes it easy to download DLCs, too, in a GUI available in many languages. You can download freeShop here.