At 1xINTERNET, we manage hundreds of drupal sites, some of them in them in Drupal 7, others in Drupal 8 (and a multisite in Drupal 6 that we don't talk about).
To manage all these sites, and allow our developers to just start working on their tickets, while allowing our project management to efficiently perform QA activities, we have built a set of tools based on community best-practices that reduced the effort necessary to deploy our sites to our servers, or in some cases to client servers.
The tools we use include