CyanogenMod is based on the Android Open Source Project with extra contributions from many people within the Android community.
It can be used without any need to have any Google application installed. Linked below is a package that has come from another Android project that restore the Google parts. CyanogenMod does still include various hardware-specific code, which is also slowly being open-sourced anyway.
The source code for CyanogenMod is available in the CyanogenMod Github (https://github.com/CyanogenMod).
And if you would like to contribute to CyanogenMod, please visit our Gerrit Code Review (http://review.cyanogenmod.org).
You can also view the Changelog for a full list of changes & features.
Source Code: https://github.com/CyanogenMod
Device tree: https://github.com/Seraph08/android_...eplus_oneplus2