The TA Queue is a free service hosted by the University of Utah to help students in a computer lab be helped in an orderly fashion by instructors/TAs.
Students can login and join a queue specific to their class, and TAs can come around and help them in the order they joined. TAs can control the queue by accepting a student (signifying they are helping that student currently), removing students, activating/deactivating the queue, and freezing it (allowing no more students to enter).
It is complementary to the web client found at http://nine.eng.utah.edu.
The source code to this app, as well as the source code to the web service it communicates with, are open source.
TA Queue iOS App: https://github.com/urails/ta_queue_ios
TA Queue Web Client/Web Service: https://github.com/urails/ta_queue