Flying Carpet

Send and receive files between Android, iOS, Linux, macOS, and Windows: either over ad hoc WiFi with one device acting as hotspot, or over a network both devices are already on. No internet or cell connection required, just two devices with WiFi or ethernet chips (and optionally Bluetooth). In shared network mode, join both devices to the same network, pick a direction on each, and select what to send. The receiving device generates a one-time password and displays it with a QR code; type or scan it on the sending device and the transfer begins. In hotspot mode, one device creates an ad hoc WiFi network for the other to join, exchanging credentials over Bluetooth if both devices support it.