Android/iOS: Despite modern advancements in file transfer technology, transmitting pictures or links between two devices is still a pain. Chirp makes it as easy as listening to a two-second sound clip.
Chirp allows users to send pictures, notes and links to each other without having to designate an email address, pair via Bluetooth or anything else. It simply generates a short audio clip that any device nearby can pick up if it has the app open. While it's not good for secure transfers, per se, it's handy if you want to send files to multiple people at once.