The thing that actually worked was a multi-protocol messaging client, like Pidgin. Which I still use all the time, because most of the chat clients I have to d

The thing that actually worked was a multi-protocol messaging client, like Pidgin. Which I still use all the time, because most of the chat clients I have to develop against have introduced asinine restrictions that force their official clients to run in single-instance mode, so your other alternative is spinning up entire VMs in order to have two accounts signed in to talk back and forth on the same machine.