Chirp is a free app which allows you to share links, text or images via sound.
A simple menu gives you options to take a picture, add a photo from your gallery, type a note or add a link.
When you're done, click the Chirp button and the app encodes the data in audio form, plays it as a sound, and anyone else running Chirp in the immediate vicinity should receive your data.
That "should" is maybe questionable, as it depends on the volume of your device, the distance they are away, the sensitivity of their microphone and the amount of background noise.
Of course you need to be careful not to share anything confidential, too, as you're effectively broadcasting it to anyone within range who's listening. Although, fortunately, the app only works when it's in the foreground, so it's unlikely a stranger will intercept your message.
Note that, there's now also a Chrome extension which allows you to send links from desktops to your Android and iOS devices.
Yeah, we know, this sounds like a joke. But it works, and it could be a useful way to share small amounts of data between a group of people.