NixOS is a Linux distribution with a unique approach to package and configuration management. Built on top of the Nix package manager, it is completely declarative, makes upgrading systems reliable, and has many other advantages.
NixOS support for arm64 is experimental. The community is very active, with one of the busiest projects on Github tracking package updates. As part of the effort, there is a community build server running on the Works on Arm cluster to speed up local development by running arm64 on a 96-core Cavium ThunderX system and armhf (32-bit Arm) jobs on a Hisilicon Hi1616 system as of September 28, 2018.