Book2Read is a universal link for eBooks (it finds all stores selling your book). It’s by Draft 2 Digital but you don’t need to be published via their platform to use it.
Your potential reader then chooses the shop they prefer and are taken to your ebook to buy there.
BookLinker is a universal link for Amazon. It links people to your ebook at their ‘Zon. Amazon often links the various formats together so they can chose if they’d prefer paperback or hardback, etc.
You could lose a potential reader if your link took them to a ‘Zon of another country because they might not have time to search for it again on their ‘Zon.
BookShop.org (US/UK only) links to your book at the readers local indie book shop.
This is great for two reasons. Reason one, you are keeping beautiful local bookstores alive by sending customers their way. And reason two, if you create an affiliate store, you earn 10% on referrals’ purchases.