Ok, but surely that's not used for IPC.

Nowadays many people do indeed use JSON over HTTP for IPC - it's the lifeblood of microservices.

More efficient protocols are also used of course, such as Cap'n Proto, Protocol Buffers etc.

Ok, I get if they're looking to scale and have them on multiple machines. But I tend to use namedpipes and/or shared memory because I need fast access between multiple services on the same machine. I don't need to scale.

You can use named pipes without WCF[0]. Sample here[1].

I've also used the IpcServiceFramework[2] before, and it worked a treat.

[0] https://github.com/dotnet/docs/blob/master/docs/standard/io/...

[1] https://github.com/GustavoHennig/PipePoc

[2] https://github.com/jacqueskang/IpcServiceFramework