Well all of us have worked with a team on a project at this point, that's kind of what we do. Isn't it terrible when you look at someone else's code and it seems they've forgotten everything they know about programming, or maybe that they just never knew anything?
CodeJar is a collaboration webapp that allows team members to review the code of the other members and assign predetermined 'fines'. These fines subtract from an initial deposited amount and pretty much say 'you're paying for this much of our pizza on Friday before we split it.' When these are applied it sends an email to the fined user and tells them who fined them, what chunk of code they were fined for, and a comment to help them avoid the mistake in the future.
In codejar we used the GitHub, Venmo, and Mailjet APIs in order to make the process of gathering information, keeping track of files, sending emails, and managing transactions as fluid a process as possible.