Is anyone aware of a simple peer-to-peer voice chat software to talk between two Linux clients on the same subnet? Actually, one peer is on a TUN VPN, but there are routes set up so the two clients can access each other. So effectively, I think I can treat this the same as the "same subnet" case. If not, I can always set up a TAP VPN instead.

I don't want something that requires logging into a third-party server, or even a local self-maintained server. No address books. No file transfers.
No fancy features (although echo suppression to stop feedback would be nice).

Just something where 192.168.0.2 can talk/listen (in the "voice" sense of the word) to 192.168.0.3. Preferably using a speaker and microphone as opposed to a head set (that's why feedback suppression would be nice).

I need "simple" as in "88 year old non-computer-literate-parents simple". Both client ends run LinuxMint.

Any suggestions? Does such a thing even exist?

I don't think so. It still has to be voip, even though it's on the subnet. A search for peer to peer voip turns up nothing of what you specified.

Thanks for the reply.

The closest thing I've found so far is Mumble/Murmur. But you have to run a Murmur server, but I don't think this requires and external login creation or third-party website. I'm investigating. My client end has plenty of horsepower, but the other client end - not so much. I'll have to do some testing.

It depends how bad you want it. There is a program called ztalk, and its GUI, Xztalk, which will do what you want. But I'd be more inclined to just buy a couple of cheap radios than use ztalk.