You can still find it in very few places. Like Google Groups (see example). But even that, understandably, is getting a redesign, one that hides quite a bit of functionality and seems to dispose entirely of some (e.g. some filter options).
I recall it was a "thing" with some PR work popularizing its launch across different Google products as a unification of their interface designs. I can't recall its name and no query gets me anything similar. And sadly there's no such thing as a compiled "history" of design languages used by a company even one as big as Google.