I was trying to find that open-source file transfer app that I used a few times during the development of no signal. Apparently I forgot to note it; it's Warp. It's part of the GNOME Circle, a set of applications which extend the GNOME ecosystem and are showcased and supported by GNOME.

I think Warp is the best file transfer program I've used. It says that it transfers files encrypted, but I'm not sure if this means it's E2EE.

Unfortunately, Warp a common word which makes it hard to look up (the top results included a terminal with AI agents built-in).