Scratch substitutes the program source code for a series of pre-defined instructions that can be dragged and dropped within the development area. Instructions like loops and control sentences like 'if' or 'case' are used to nest the rest of the operations in a graphic form.
Each group of commands corresponds to a color code. So, those that deal with movement are in blue; those that deal with sound, purple; and those that deal with control, orange.
Additionally, some instructions permit variable perimeters, which are possible to see in numeric form over the surface. You can use the sprites included with the application or draw your own from the program's drawing window.
Scratch is designed to complete small programs, although on its website you'll also find some really impressive projects.
For Mac OS X 10.3 or later.