The Barnes & Noble NOOK Tablet has a locked bootloader, which has prevented hackers from figuring out how to replace the version of Android that comes on the tablet with custom software such as CyanogenMod. But that doesn’t mean it’s impossible to run an alternate operating system on the NOOK Tablet.
In fact, you can now install and run Ubuntu Linux on the NOOK Tablet. There’s just one catch: What you’re actually doing is loading the operating system onto an SD card and then remote-controlling it using a VNC app while running Android.
In other words, you’re running an operating system within an operating system.