ROMs are great but most of the ones out their vary very little one from another and it is hard to choose just one. With MultiROM for Nexus 6 you can install multiple ROMs on one device and easily switch between them, the multi-boot mod has been available for some time but just now made compatible for the Nexus 6.
With MultiROM For Nexus 6 you can boot any Android ROM (like Cyanogenmod, Paranoid Android etc. ) as well as other systems like Ubuntu Touch, once they are ported to that device this also includes Microsoft’s future Windows 10 OS for Android.
How to install MultiROM For Nexus 6

- Download the app here
 - select MultiROM and recovery on the Install/Update card
 - If the Status card says Kernel: doesn’t have kexec-hardboot patch! in red letters, you have to install also patched kernel
 - To add a ROM boot into recovery
 - Select “MultiROM”
 - Add ROM. Select the ROM’s zip file and confirm
 - Once done, reboot your device
 - You will now boot into the selected ROM
 

