The OnePlus team has released OxygenOS for its OnePlus One smartphone. Based on the Android 5.0.2 Lollipop, the OxygenOS is developed by giving prime importance to performance and battery life over gimmicks and bloated features and at the same time, it keeps most of the original features in the OxygenOS, such as double-tap to wake, music controls, and shortcuts for the camera and flashlight.
According to the developer, “the main goal for OxygenOS is to provide faster, more meaningful updates and a better-integrated range of services for every OnePlus user”. However, the main decision following the release of OxygenOS may be due to the controversy with CyanogenMod licensing in India.
OxygenOS is based on the ASOP (Android Open Source Project) and this version of the custom ROM is built on the Android 5.0.2 Lollipop. It is free from bloatware apps, and has near stock interface. In this guide, we show you how to install OxygenOS on OnePlus One.
Important: As always, backup entire data on your phone before installing this ROM. Also, make a full system backup (Nandroid backup) from custom recovery.
1. Install custom recovery like TWRP [HERE]
2. Download OxygenOS [HERE], unzip it and transfer the oxygenos_1.0.0.flashable.zip to your phone
3. Turn off your OnePlus One and boot it into custom recovery by holding down both the volume down key and the power button.
4. From recovery, do a factory reset, cache, and Dalvik cache
5. Now, go to Install and locate the ROM zip file you copied to your device and confirm flash.
6. After the successful installation, reboot the device, which will take you to the new OxygenOS. Enjoy! (Source)