Earlier quoted context omitted.
For that application, Web Wormhole is unbeatable: https://webwormhole.io/
But here you download the source code every time you use it. It's not end-to-end anymore, as the person who designed the website can deliver malicious code, unless you pin the JS somehow. I wish magicwormhole or croc came with every major OS preinstalled.
I'm not aware of any other major OS ;)