In working on Brie, I had been vaguely aware that the 'Self' language was similarly based on copying prototypes rather than instantiating classes. So I kind of went 'yeah, whatever' when Rick McGeer and others told me to check up on this '80's Xerox PARC project.

Wow. I hadn't realized that Self was so close in both the domain and the solution spaces. If there's interest I'll try to produce a comparison later, but for now, check out the Self site and, in particular, this paper.