TIL you can transfer files using a QR Code, without WiFi or Bluetooth, even on airplane mode. Although it is slow (200KB/s) it is usable.
Decimen encodes the file into fountain-coded QR then you scan it, decode it on another device then you can "get" the original file. If you are watching this on your PC, you may scan the flickering QR Code in this video and you can receive the same file from me.
The advantage of this project is that the encoding and decoding are all done in your browser. There is no need to install any apps. However it requires a good phone camera to make the scanning successful or the transfer will become very slow. Tested on my budget Android phone, I need to lower the QR code FPS from 60 to 10 or it cannot decode.