Simula
The Simula programming language was a predecessor to Smalltalk.
Simula was designed for simulations, and the needs of that domain provided the framework for many of the features of object oriented languages today. Simula was developed in the 1960s at the Norwegian Computing Centre in Oslo, primarily by Ole-Johan Dahl and Kristen Nygaard. It resembles Algol60 in a lot of ways and was probably based on it. It adds features that go almost to the modern idea of classes and objects. It also adds coroutines. Simula is still used a little for serious work as of 2003, but it is probably fair to say its historical influence is more important than actual work being done with it.
A successor to Simula named BETA was created but is used even less.