Libby - I used to buy so many Kindle books and had an expensive Audible subscription a year ago but all that stopped when I discovered Libby. I can read ebooks and audiobooks right in the app using my local public library card for free and the entire UX of the app is just beyond awesome. I can now read/listen to 5-7 books a month using Libby.
The winning combo for me is Libby + Hoopla + Library Extension for Chrome. Anytime I see something I'm interested in on Amazon, Goodreads, etc. - I immediately see (and can store for later reading/listening) if it's available via my local library. Can't count how many books I got this way, totally free.
Libby is pretty much same as Overdrive just in a nicer package. In fact it's developed by the same company that created Overdrive so you can easily switch from OD to Libby. And I'm sure you won't regret as Libby has such a great polished UI compared to OD.
The e-ink eReaders from Kobo have an integration with Overdrive, which is by the same company as Libby. Kindles are designed to sell you more books from Amazon.