Meh, S3 is nice and lightweight for a very particular kind of analysis interoperability. S4 isn't super useful IMHO. RC is very well thought out, and I've heard

Meh, S3 is nice and lightweight for a very particular kind of analysis interoperability. S4 isn't super useful IMHO. RC is very well thought out, and I've heard good things about R6. It might not be sane language design, but it works well for designing very different kinds of analytical procedures.