The Google Nexus 7 tablet produced by Asus is an Android tablet that you can get with affordable price. It can run both Android and Ubuntu. The problem is how to select operating system that you want to run at booting.
A solution called multiROM allows you to install some operating systems on Nexus 7 tablet, so we can select the operating system at booting.
If you want to do that, do it at your own risk cause you can lost all of your data or damage the hardware as it’s related to boot sector and data partition.
MultiROM developer plans to add booting from external drive (such as USB flash drive or hard disk) support. Cause the tablet doesn’t have a microSD slot, it’s impossible to boot from SD card.