gbooch writes "The Computer History Museum, located in Mountain View, California, is not only a museum of hardware but also a museum of software. As reported by Arik Hesseldahl of Bloomberg today, with the permission of Apple Computer, the Museum has made available the original source code of MacPaint as well as the underlying QuickDraw graphics library.
MacPaint was written by Bill Atkinson, a member of the original Macintosh development team. Originally called MacSketch, he based it on his earlier LisaSketch (also called SketchPad) for the Apple Lisa computer. Bill started work on the Macintosh version in early 1983. He also created QuickDraw (then called LisaGraf) for the Lisa. Andy Herzfeld, another key member of the team, considers QuickDraw "the single most significant component of the original Macintosh technology" in its ability to "push pixels around in the frame buffer at blinding speeds to create the celebrated user interface."
MacPaint was released with the Macintosh in January, 1984. The application was written in Apple Pascal and was packaged in a single file of only 5,822 SLOC, together with an additional 3,583 lines of assembly code for the underlying Motorola 68 microprocessor, used to implement routines needing high performance as well as certain interfaces to the operating system. QuickDraw was the Macintosh library for creating bit-mapped graphics and was used by MacPaint and other applications, and consisted of a total of 17,11 lines of 68 assembly code packaged in 36 files."
Link to Original Source