Google Tone is a Chrome extension that allows you to share urls with the click of one button. It uses the computer's microphone to transmit a sound. Other computers in the room that have Google Tone installed and are in proximity of the sound can then hear the sound.
I've used Google Tone as a way to collaborate with a colleague that is sitting next to me. Instead of emailing links back and forth or pasting them into a Google Doc, I can click on the Google Tone icon and the person instantly has the link. It makes sharing information more efficient.
In the classroom, it would be more complicated to use. Since it depends on sound, a classroom full of students that are talking would mean the Google Tone might not hear the sound. Also, anyone with the extension can share links. Keeping students from playing with it would be distracting and hard to do. It would however, work for students working together in a small study session, but not for a full class.