Free apps account for nearly 90 percent of total software downloads. In 2012, there were 40.1 billion free downloads and 5 billion paid downloads. Most of the paid downloads cost less than three dollars. You will choose an app or other piece of software that you enjoy and “reverse” engineer it. You will write requirements for at least two features of the software, then prepare a slide show or video to explain the requirements and how the software is used.