Is GrapheneOS the first one to do that? What's special?
Discussion
LineageOS, launched in 2016, is a direct fork of CyanogenMod and is known for its stability, security, and customizability.
CalyxOS, launched in 2018, and GrapheneOS, launched in 2019, both are a privacy-focused ROM that provides a more secure and private version of Android.
GrapheneOS started in 2014 and was previously called CopperheadOS due to a sponsorship by an abusive, malicious company. GrapheneOS is a continuation from the original team and the product with the older name is now a low-effort proprietary fork. Original CopperheadOS is GrapheneOS.