=== [https://alpinelinux.org/ Alpine Linux] ===
The minimal Linux distribution
, that postmarketOS is based on. Actually, pmOS only adds a few packages on top of it, and provides the installer and development environment - that is the plan, to keep following upstream as close as possible. Alpine developers do not see their distribution as "GNU/Linux". That being said, it works a lot like a typical Desktop Linux distribution. You have your package manager, the typical shell commands, you can install typical Linux software, and so on.
=== android-msm ===