The Barnes and Noble Nook HD and Nook HD+ run customized versions of the Android operating system with their own App Stores. While they are available at very competitive prices, it is sometimes hard to choose one of these tablets due to the lack of official apps on their store compared to the vast number of apps available to Android tablets through Google Play.
However it looks like this is about to change as a new OTA (over-the-air) update which is being released for these tablets brings access to the official Google Play Store.