Basically it's a simple open-source app that you can create your own flashcards on. The neat thing about it is, as I said before, is the algorithm which is designed to work using spaced retrieval. In essence, after creating the cards, you review a few of them daily, rating them 1-4 each time you see them depending on how easily you remembered the answer for the flashcard. Based on this response and previous responses to the same card, the algorithm then decides for itself when it will show you the card next. This is more effective than normal flashcarding as it is more efficient, since you don't have to go through the entire deck each time, and actually picks the correct intervals for promoting long-term retention rather than how well you 'think' you know the card. It also makes sure you don't forget cards you think you know really well. It is cross platform, syncs nicely, and is easy to share with others as well. No ads, no internet required if you are using it on one device, and has a refreshingly minimal UX. The others are just added bonuses though, it's really the algorithm that makes anki effective in a way that notereading or traditional flashcarding is not.