Correct. Moby uses containerd because Docker uses containerd.
> which I guess is not related to systemd
You guessed correctly.
> even though systemd also has its own container system
Correct I believe systemd uses a tool called nspawn to isolate processes in containers. We don't use systemd/nspawn, but I think it would be a cool customization to build a Moby assembly that uses systemd.
> Are there any components to moby that are OSS
All Moby components are open-source.
> and a part of the linux stack
All Moby components run great on Linux.
> or is this whole endeavor to break away from linux dependencies?
Moby works great with Linux and will continue to. In fact you can build a complete custom Linux system with Moby, thanks to LinuxKit. (But you can also target an existing Linux system, LinuxKit is optional).