Collaborative tools can be as complex as a source code version control system or as simple as a collaborative word processor. Team roles in pair programming are driver and navigator but students can take on more specialized roles in larger teams. Teachers or students should choose resources that aid collaborative program development as programs grow more complex. For example, students might work as a team to develop a mobile application that addresses a problem relevant to the school or community, using appropriate tools to support actions such as: establish and manage the project timeline; design, share, and revise graphical user interface elements; implement program components, track planned, in-progress, and completed components, and design and implement user testing.