Check out these APIs for use in developing NOOK apps.
NOOK SHOP Details API
NOOK SHOP Details API provides an easy way for you to cross-promote your apps within any given application. NOOK provides a SHOP Details intent, which allows you to open up an overlay in your application directly to the product details page for a specific item in the NOOK Storefront. Users can then buy the item directly from that page, or can close the overlay and simply return back to your app.
Please note that NOOK only allows linking through NOOK SHOP Details API. Apps cannot use external links or any other method to distribute your other apps or content within your app.
NOOK devices support both static and live wallpapers. To supply apps that support the NOOK wallpaper API, follow the process here. Note that the actions are different for NOOK HD and NOOK HD+ than for NOOK Tablet and NOOK Color.