I think Ruby qualifies as true OO (in the Alan Kay sense) because messages are first class entities that can be explicitly manipulated. This makes it trivial to

I think Ruby qualifies as true OO (in the Alan Kay sense) because messages are first class entities that can be explicitly manipulated. This makes it trivial to implement lots of OO patterns that require a significant amount of boilerplate in other languages. For example, a proxy. Erlang makes messages an even more central element, as the whole language is built around the concept of inboxes and asynchronous message passing (synchronous message passing being a special case). Better type systems are in vogue now, for really good reasons. But I wish we don't ignore lots of good ideas from dynamic languages like Erlang or Mozart/Oz. Every time I open CTM or SICP I find great insights I had already forgotten.