Migrating off a closed custom CMS onto WordPress, without losing a single ranking. Content, structure, and URLs moved over one-to-one, and the client got an admin where they edit services, locations, and copy themselves.
The old site ran on a custom CMS with no code access and no way to add a new service page. Every change went through the previous developer.
I catalogued every page and URL, mapped them to the new structure, and rebuilt the site on a WordPress theme, with services and locations as separate pages. Redirects went live before launch, so no address was left dangling.