I have some good news for you today: Mike Cane has tipped me to a competing service. Launched in May, Boook.link is a service that authors can use to find all of the websites that carry their books.
It’s not quite as comprehensive as its competitor yet, but the developer is adding more stores all the time. What’s more, as you can see on this page, Boook.link also includes links to WorldCat and GoodReads as well as sites that sell the print book (AbeBooks).
Clearly Boook.link was built with an entirely different purpose in mind than was Draft2Digital’s Universal Links feature. To put it simply, if you want to link to ebook retailers, use Draft2Digital’s Universal Links feature. But if you want to link to all types of sites where your book can be found, check out boook.link.