I've used fldigi between two computers in the same room. It's also made for amateur radio, but when we do training, we just get operators to setup their laptop

I've used fldigi between two computers in the same room. It's also made for amateur radio, but when we do training, we just get operators to setup their laptop in the same room. If they have external headphone, that works best since you can basically lay then mic to speaker. But we'll often take turns having one blast out a message over speakers and everyone else receive it. https://sourceforge.net/projects/fldigi/ https://sourceforge.net/projects/fldigi/