It's a fork of LineageOS, which is the daughter of CyanogenMod, which is a fork of Android.
Only difference when comparing against LineageOS is that the OpenGApps package is "free".
Only difference when comparing against LineageOS is that the OpenGApps package is "free".
Rather GApps (google) functionality is re-implemented from scratch and the necessary means (app signature spoofing) to replace GApps with microG is built into this LOS fork