Okay, not very many people are going to use this app, but the fact it is available at all is a major step forward for B&N.
I have been wanting to see library ebook apps in the Nook App Store ever since I returned my Nook Tablet last fall. This was, in fact, one of my major gripes. At the time B&N didn't exactly seem happy about allowing any competing reading apps, no matter where the content were coming from. Heck, B&N didn't let Readability into the Nook App Store until June, and I have been told that the OverDrive app had been stuck in the approval process since February of this year.
On the other hand B&N did allow the Pulse news aggregator app into the Nook App Store in early 2011, so perhaps B&N just has a long and contemplative approval process. In any case, the reading options on the Nook Tablet and Nook HD continue to expand.
You can also find this app via Google Play.