There are some books that are more general knowledge and cross over to other sports. My favorite is, " The Talent Code: Greatness Isn't Born. It's Grown. Here's How." By Daniel Coyle.
Honestly, I think what you're looking for, you'll actually find more of on sites such as this one by looking and searching older threads and topics that interest you and it won't cost you a dime. You'll find numerous books and e-books on softball's specific topics such as strategy, hitting, catching, throwing, etc. etc. However, a word of warning. Through the use of slow motion cinematography, many of the former instruction/drills/mechanics are now considered out of date if not completely wrong.