The last part about the stack overflow account and forum account is about the infamous silk road admin, Ross Ulbricht

Syncthing and LocalSend.

Syncthing is used if it is not a one time transfer. LocalSend is mainly for one time transfer. LocalSend needs things to be in the same network. The same WiFi router is enough. Syncthing can send files over the internet also.

There are browser based alternatives like ShareDrop . These tools are not as reliable as Syncthing and LocalSend, especially when it comes to single large files (more than a few GBs), like ISOs.

For one time transfer over the internet, another handy tool is Croc . This one also suffers from the large file related issues.

https://ente.io/

I think this is very close to what you are looking for. Recently they have open sourced all their server side code also. Means currently they are completely open source.

That comment is just speculation… In fact many of the Adguard employees are from Ukraine and other not so pro Russian countries. I remember their support being almost stale when the war started.