CyanogenMod (often abbreviated "CM") was a popular[12] open-source operating system for smartphones and tablet computers, based on the Android mobile platform. Although only a subset of total CyanogenMod users elected to report their use of the firmware,[13] as of 23 March 2015, some reports indicated over 50 million people running CyanogenMod on their phones.[12][14] It was also frequently used as a starting point by developers of other ROMs.[citation needed]