Barnes & Noble has for some reason left a loophole open on their Nook Tablet.
Users can install third party apps by download APK installer files using the web browser on the device.
And this allows them to install third party launchers and even the Amazon AppStore!
It is not clear if this loophole was left open by choice or accidentally. Barnes & Noble might close it in a future software update.
Barnes & Noble does not offer many free apps through their official app store for the Nook Tablet. This is a good way to get third party apps from the web.