An application developer is responsible for developing and modifying source code for software applications. These applications are aimed at aiding customers with computer tasks or programs.
QA analysts/testers are responsible for the testing phase of the production process to ensure that final products meet the company standards. Duties include identifying whether products are functional, reliable, and meet the end user's expectations.
Programmers are responsible for writing the code that makes up computer software. They are tasked with defining the workflow of a program, writing the code, testing the program functionality, and creating documentation for the program.