Rootssh from Mac OS with Homebrew fails with netcat

Yes, xdg-open is a Freedesktop.org thing (Linux only, I guess). Given that it depends on the XDG specification, I would not try to install it on anything that is not GNU/Linux.

xdg-open basically takes care of spawning the associated application to deal with the specified file/URL. Given that it is the used in rootssh to open the default browser, I guess you can achieve the same effect by using the macOS open command as in:

$ rootssh --browser open seligman@myserver

I will create a GitHub issue to improve the rootssh script on macOS (CC: @linev).

Cheers,
J.