Voplo, the five-stranger humming exchange

Field notes

The service uses short-lived, randomly routed recordings rather than follower graphs or public feeds. A hum can reach up to five listeners, each listener gets one playback, and the recording returns to its sender after all five respond or 24 hours pass, then remains available for another 24 hours before deletion. The terms also specify that unopened received hums expire after 48 hours and that users must be at least 14.