I don't know about the rest of the software but Mattermost is easy to administer and requires minimal babysitting. I have it deployed with a simple docker-compose file which I only touch when I want to upgrade it, and there are Helm charts if you want a more production grade deployment. If I were to deploy it for my company I'd probably use the helm chart + a cloud hosted Postgres as the database and would likely never have to touch it between upgrades.