Is your device rooted? Then you know what CyangenMod is. If so you might have CyangenMod installed on your device.
The insanely popular custom ROM for Android has been downloaded over 10 million times so far. Out of those, the official downloads are about 5.6 million (which are basically “official” CM builds). Meanwhile, unofficial download count is around 4.5 million (refers to CM ports for unsupported devices)