Application IconsOne of the innovations that NeXT came up with was the concept of a Dock on the main screen, where Icons of a frequently used applications could be placed. Clicking on the icon launched the application. The Icon was actually a link to where the application was in the file system and it saved a lot of clicks each time the application was needed.
Creating attractive Icons was a point of honor for application developers with much thought going into capturing the essence of the application in a single 48x48 pixel monochrome image. Later when the color machines were introduced and 64 x 64 pixel images were possible, the arms race began again with an industry of "Icon creating" experts and companies popping up.
Below are 300 of the best. Where there are seemingly duplicate or triplicate images, all were used as a single Icon to represent different states of a mouse click on color and mono screens .
While Macs and PCs all have this today, the Icon Dock and different icon color to represent the state of an application to place most used applications, was to my knowledge first used on a NeXT Computers.