MultiROM for multi boot

http://www.droidviews.com/multirom-for-nexus-6/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+Droidviews+%28Droid+Views%29

Better to read the XDA thread, with more details:

XDA: http://forum.xda-developers.com/galaxy-s4/i9505-orig-develop/mod-multirom-v28-t2864469