Wikipedia
CyanogenMod , usually abbreviated to CM, is an open-source operating system for smartphones and tablet computers, based on the Android mobile platform. It is developed as free and open source software based on the official releases of Android by Google, with added original and third-party code. It is based on a rolling release development model.
CyanogenMod offers features and options not found in the official firmware distributed by mobile device vendors. Features supported by CyanogenMod include native theming support, FLAC audio codec support, a large Access Point Name list, an OpenVPN client, Privacy Guard (per-application permission management application), support for tethering over common interfaces, CPU overclocking and other performance enhancements, unlockable bootloader and root access, soft buttons and other "tablet tweaks", toggles in the notification pull-down (such as Wi-Fi, Bluetooth and GPS), and other interface enhancements. CyanogenMod does not contain spyware or bloatware, according to its developers. CyanogenMod is also said to increase performance and reliability compared with official firmware releases.
Although only a subset of total CyanogenMod users elect to report their use of the firmware, as of March 23, 2015, some reports indicate that over 50 million people run CyanogenMod on their phones.
In 2013, project founder Steve Kondik announced that venture funding had been obtained to establish Cyanogen Inc. as a commercial enterprise to develop and market the firmware more widely. This announcement has led to controversy within the community, with some developers asserting that rights and licensing issues, acknowledging/compensating past developers and honoring the original ethos of the community project, are not being adequately addressed. These claims were rejected by Kondik, who affirmed support for the community and stated that most CyanogenMod code, as with Android generally, is bound by a non-restrictive Apache license.