Ivan Sutherland created a computer program called Sketchpad in the early 1960's as his PhD thesis. These were the days of punch-card programming, which meant that making a complex interactive program was extremely challenging -- particularly if it needed to use an interactive Graphical User Interface, which was unheard of at the time. But that's what Sutherland did -- Sketchpad was an interactive drawing program in which the user drew with a light-pen while pressing switches alongside the screen. Sketchpad basically invented a category of software -- Computer Aided Drafting, or CAD -- and it all ran on a 1958 computer with roughly 272k of memory. (By comparison, the laptop I'm typing on now has 15,420 times as much memory, but no light pen.)
In the video below, computer pioneer Alan Kay discusses a famous video of Sutherland's Sketchpad demo. This is some nerdy, but important, computer history. Kay says: "I once asked Ivan Sutherland: 'How could you possibly have done the first interactive graphics program, the first nonprocedural programming language, the first object oriented software system, all in one year? He said, 'Well, I didn't know it was hard.'"