The Omni Rom brings a stock Android experience to your device. As they put it, "it's not better it's just different." The rom has just been updated to Android 6.0 Marshmallow on the OnePlus One. This rom brings optimization and some customization options. It's pretty awesome that the dev community is able to get the latest and greatest version of android on the OnePlus One before the OEM! The phone officially runs CyanogenMod 12.1. To install this rom you will need to have a custom recovery installed and you will need to be sure to grab the GAPPS package. Head to the link below for the necessary files.
via XDA