Mirroring an entire website is trivial, but the concept of continuing one on afterwards seems a world away from regular open source efforts where it's a daily o

Mirroring an entire website is trivial, but the concept of continuing one on afterwards seems a world away from regular open source efforts where it's a daily occurrence. I'd be interested in how many sites were "forks" of an original, doubt there's many at all apart from SEO spam?