One nice aspect of z-lib was that they would provide recommendations for books on the download page. I found a bunch of books on category theory that I wouldn't

One nice aspect of z-lib was that they would provide recommendations for books on the download page. I found a bunch of books on category theory that I wouldn't have found any other way. Not sure what they were using for the recommendations but the algorithm was much better than other book recommendations, e.g. Amazon's "other people also bought this".