In addition to prototype based OO, you have also implemented Ruby-style singleton methods (aka - Eigenclasses). This is also the same mechanism Perl 6 will use for runtime role composition. In short, you've stumbled onto something very useful :)

One suggestion though, you might want to think about doing this in a more dynamic fashion. Meaning, do not create the unique class until you absolutely have too, (which would be the first call to &install). This would allow you to get rid of &new entirely, which would make this module (IMO at least) easier to re-use since you would not have to remember $self->SUPER::new() all the time.