> Philosophically, Smalltalk's objects have much in common with the monads of Leibniz and the notions of 20th century physics and biology

Love this line as this was definitely my impression of monads when venturing into Haskell-land...

The whole history of Smalltalk is interesting and it's an interesting way to reason about data and behaviour. And even if Smalltalk is obscure, C++, Java, Ruby, Python and others aren't, and OOP remains a great way to model many domains.