Classroom Presenter

Richard Anderson has been working on a very simple, but useful, classroom sharing technology called Classroom Presenter http://www.cs.washington.edu/education/dl/presenter/
It is open source. It is intended for whatever media kids bring to the classroom, but his experiments have been with tablets.

A teacher can broadcast a question and students working in teams answer using a simple sketching utility. The teacher can see thumbnails of each presentation in a 'film strip' format on the left of his/her screen, select any one, and send it on to the projector so everyone can see it (why not send it back to everyone and save a projector?) The public version is anonymous—this is important to encourage students to contribute. There is often competition for making the contribution that is chosen for sharing. Some students put icons on their work so they and their friends can know who is selected, while still being anonymous.

This is in the category of things that are easy to do but useful, particularly in the teacher-centric classroom.