CyanogenMod

CyanogenMod is an operating system for many smartphones and tablet computers. It is based on the Android operating system. This means all of Android's programs (called "apps") can be used with CyanogenMod. 
Because it is Open sourced it can be changed. It provides more options for a smartphone or tablet computer than with normal Android.
But CyanogenMod is more difficult to set up than other similar operating systems. This is why most of CyanogenMod's users know more about Android than the normal Android user.
CyanogenMod can be installed from this link . Also, some phones, such as the , come with CyanogenMod as its default OS.