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Uses WebRTC for file transfer.

Just to make it more obvious: You don’t have to self host it, there is a free (no registration) Version deployed at https://sharedrop.io

Works perfect between IOS, Android, Linux, MacOS and Windows.

Why does it need firebase? That doesn't seem to tic the "not-google" box. :-)

FilePizza also uses WebRTC without Firebase - https://file.pizza/