Logic-immo.com is the second most visited real estate website in France. I was hired in 2012 to join the maintenance team on the main website, which was at the time written in plain PHP (no framework whatsoever), and an old JS framework called MooTools on the frontend. The job was not easy, but it certainly was educational!
Realizing the instability of their flagship website, the company executives decided to migrate the website to a more modern and scalable solution. We recommended to go with Zend Framework on the backend, and SASS, Bootstrap and jQuery on the frontend. My role in this was to train the team to those new libraries, tools and workflows, and oversee the frontend developments in general.
It was in 2014, styleguides were seriously starting to emerge. Since we were in a complete do-over, we decided to build our own styleguide that would be shared among all the websites of the brand. We took the idea pretty far: every component was to be developed as a standalone partial in a module hosted in its own git repo, to be included in the other projects as a composer dependency. It helped us achieve consistency among all properties, despite the pretty heavy workflow for the developers.