It may be a custom shell, written specifically for the project, or more likely, a variation of that using a multimedia delivery tool, such as iShell, Director or Authorware. Web pages are created and tested or scripting for the multimedia tool is done. Screens are designed and laid out. Interactivity is added to each button, slider, test screen, and animation. This phase requires not only engineers skilled in the tool itself, but an understanding of pedagogy - the teaching and learning process itself.
Production is an exacting discipline, requiring experience, skill and patience.
Both asset creation and production each require about the same amount of time in any given project. One of the later stages is testing on various platforms. This requires that we have all the various operating systems and computers likely to be found. The product is placed on its final media, and tested against the platforms on which it is designed to run. Errors are corrected and the process is repeated until the in-house tests are all passed.