OnePlus announced their fourth smartphone (OnePlus One, OnePlus 2, OnePlus X and now OnePlus 3) back in June. It was made available immediately, which made plenty of buyers excited. Since most smartphones are announced and then not available for weeks and sometimes months. The OnePlus 3 has rather high-end specs, for it's $399 price tag. Including a 5.5-inch 1080p display, Qualcomm's Snapdragon 820 processor, 6GB of RAM and 64GB of storage. Making most people excited about this device. However, not everyone loves the software on the OnePlus 3. OnePlus has been using Oxygen OS on their smartphones, since the release of the OnePlus 2 - and it made its way to the OnePlus One shortly before its successor was announced. It's mostly stock Android with a few tweaks. But if you aren't a fan of Oxygen OS, there's an alternative.
While the OnePlus One launched with Cyanogen OS pre-installed, every smartphone from the company since then has not. But those with the OnePlus 3 will be able to toss on a CyanogenMod 13 nightly and call it a day. This is the open-source version of Cyanogen, and CyanogenMod 13 is based off of Android 6.0 Marshmallow. Which is currently the latest version of Android - with Android 7.0 Nougat due to launch in a few weeks. Keep in mind that this is indeed a "nightly" which means that there are likely plenty of things broken, within CyanogenMod 13. But if you are brave enough to install it on your OnePlus 3, you'll likely get a pretty amazing experience.
For those that may be unfamiliar with CyanogenMod or any other custom ROM, it essentially replaces the software on your smartphone. CyanogenMod 13 would replace Oxygen OS and give you all the features that are included in CyanogenMod 13, which itself is mostly a stock Android operating system as well. Of course, you will need to root your OnePlus 3 to install CyanogenMod 13 onto your device, so it's recommended that you look up how to do that first. Also keep in mind that if you want Google services, you'll need to flash the latest Gapps with the latest CyanogenMod 13 nightly. All of that can be found in the source link below.