Armbian is described as 'base operating system platform for single board computers (SBCs) that other projects can trust to build upon' and is an app in the OS & Utilities category. There are eight alternatives to Armbian for a variety of platforms, including Linux, Windows S, Arch Linux, Nix Package Manager and Raspberry Pi. The best alternative is Ubuntu, which is both free and Open Source. Other great apps like Armbian are Arch Linux (Free, Open Source), Raspberry Pi OS (Free, Open Source), MerOS (Free, Open Source) and Archcraft (Free, Open Source).
Ubuntu is a community developed, Linux-based operating system that is perfect for laptops, desktops and servers. It contains all the applications you need - a web browser, presentation, document and spreadsheet software, instant messaging and much more.
Arch Linux is an independently developed, i686- and x86_64-optimised GNU/Linux distribution targeted at competent Linux users. It uses pacman, its home-grown package manager, to provide updates to the latest software applications with full dependency tracking.
MerOS is a user friendly, good looking, general purpose Nix based GNU/Linux distro. It is ideal for those who want the most out of their computers, a well-designed desktop environment and an uncommon Linux experience.