File sharing software with the following characteristics:
- Works on most platforms
- Lossless media sharing
- May require internet connection, but only to discover devices
- Fast transfer speeds
- No GPS, Bluetooth or WiFi required
- Open source
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You could try just setting up an HTTP server, and then you can use the files via their URLs. If you're using media files, you might try using mpv to stream those URLs (or playlists of them). See my answer to another question for details about how to use mpv on the command-line on Android (the mpv site has information about other ways to run it).
No Internet would be required, but you would need a local network. You could use CAT6 cables instead of WiFi.
mpv is open-source and cross-platform, and the HTTP server's platform wouldn't matter.
Or, if you don't like http, I imagine ftp might work. I haven't tested ftp addresses on mpv, though.
Snapdrop has these characteristics. It is a web app, so, it can work on almost all new platforms.