CyanogenMod

CyanogenMod was the most popular custom Android-based ROM for Android smartphones from 2011 until 2016 when Cyanogen Inc. shut down the project. Since then, much of the project has carried on under a new fork called LineageOS, which continues development for popular smartphones. CyanogenMod was a revolutionary ROM for Android because it gave the user more granular control over the customization and security of their device. The ROM was based on stock Android, but it added plenty of features that eventually became adopted by Google into stock Android. Those features include gesture controls, granular audio controls, and more customization features for the actual UI. Some features like the LiveDisplay, which used ambient sensors to control the display and adjust color and saturation settings, hasn't been replicated in any other ROM that's available for Android. This feature gives you accurate color representation on your screen based on your surroundings. In fact, CyanogenMod got so popular that Chinese phone manufacturer OnePlus formed a partnership with Cyanogen Inc. to ship their phones pre-loaded with the Android ROM as their default operating system. That partnership lasted for several years until the closing of Cyanogen Inc., which caused OnePlus to switch to their current in-house OxygenOS. Today it's no longer possible to install CyanogenMod on a current device, but you can still download old ROMs for devices that received ROM support during their lifetime. LineageOS has replaced CyanogenMod in the Android enthusiast's community circle, so those hoping to run a custom OS on their device should look there as the CyanogenMod project is currently dead. Cyanogen's contributions to Android as a whole shouldn't be forgotten, and with the work continuing on LineageOS, a whole host of new devices are getting support well beyond the 24-month warranty period that most manufacturer's support.