Reading is probably my favorite activity! I'd just add that sometimes you don't want an app recommending similar books to you, you want new books, seemingly unrelated to your interests, but that you may grow to like. A good way to do that would be to, let's say, try and read the Penguin Classics series. It's all going to be different, and it's all probably going to be good. Another way is to read the 100 best books of the last century, as listed by New York Times let's say. Something like that. Our life is short and really you'll never be able to read all the books you want, so you might as well try and read the best ones.