Baseplate
Baseplate is a component library and documentation site for a team running four products with four different button styles. The work was one system, documented well enough that people actually reach for it.
Every team had quietly rebuilt the same twelve components slightly differently. Nobody had done anything wrong. There was simply no shared place to put them.
Design systems fail on adoption, not on design. Whatever we built had to be faster to use than rebuilding from scratch, or it would be ignored inside a month.
Tokens first, components second, documentation written alongside both, with live, editable examples, so a developer can see the prop they need instead of reading about it.
Every component ships with its states, its accessibility notes and its do-and-don't in the same view. Nothing lives in a separate spec that quietly goes stale.
Six thousand products, and a search that finally returns the right part.