Smalltalk made large contributions to two areas of computing, even though it is not widely used. The first is object-oriented programming. Although OO concepts were originally designed in SIMULA, Smalltalk was the first language to make full use of these concepts. However, Smalltalk is not just a programming language. The designer, Alan Kay, created an entire environment. Kay pictured a future where users could interact with small, powerful desktop machines. Smalltalk is the system which modern windowing systems are modelled after. It made extensive use of windows, a mouse, and pop-up menus. Such user interfaces were almost unheard of during the late 60's when Smalltalk was developed.

Source: "Concepts of Programming Languages" by Robert W. Sebesta, The Benjamin/Cummings Publishing Company, Inc, 1993