The Software Industry is composed of programmers, designers, marketers, sellers, and others who create the programs users need and then market them and sell them. Separated into four main categories: programming services, system services, open source and SaaS, the computer software industry has radically changed how companies interact with, develop and use software. The most common jobs in the computer software industry are software engineers, software developers, programmers, testers or quality control personnel, software marketers, sales people, and technical writers.