Alternatives

Nethserver

https://docs.nethserver.org/projects/ns8/en/latest/install.html#pre-built-image

curl https://raw.githubusercontent.com/NethServer/ns8-core/ns8-stable/core/install.sh | bash

Zextra Carbonio Community Edition

https://zextras.com/carbonio-community-edition

Univention 

https://www.univention.com/products/download/