Looks like it's matured a lot over the years since we first used this many years ago, nice clean and modern interface — the Studio is excellent and available in self-hosted (with a Pro licence, unlike Odoo where it's only available with their SaaS).
https://www.group-office.com/professional
Docker install:
https://groupoffice.readthedocs.io/en/latest/install/docker.html
TBH, the way they are offering everything installed open-source, with a 60-day trial of pro features — and relatively affordable for a business licence to respect the costs of support and evolving — it seems to be a fair and sustainable way to conduct open-source business — that seems to have resulted in a good looking, regularly updated, documented, supported, and sustainable product.
⭐⭐⭐⭐⭐
from me
Now, it only stands a chance of packaging if someone here is interested and motivated. Anyone?