And I reverse engineered enough of its protocol and made an unofficial macOS app: https://github.com/grishka/NearDrop

There's also QNearbyShare [0], a CLI implementation for Linux, which sadly can't send to Android yet, but receiving works just fine

[0]: https://github.com/vicr123/QNearbyShare

I can advocate for Trebleshot which is FOSS and available from F-Droid[0] for Mobile and Github[1] for Desktop

0: https://trebleshot.monora.org/ 1: https://github.com/trebleshot

> Still in alpha state and for this reason, nearly everything is subject to change and probably broken.

> This repository has been archived by the owner on Sep 4, 2021. It is now read-only.

Don't think this project is active anymore, and I cannot find any download links for desktop.

LocalShare seems to be available on many more platforms