Are you looking for install talkd daemon on Raspbian?
I will try to explain how to install it but before we start i just want to give a short explanation of what talkd is: it is the daemon that allow users to talk eachothers on the same machine.
Going to the code, here how to install talkd on a raspberry pi: first you need to install all the packages that we need for with the following code:
$ sudo apt-get install talk talkd
After that you will need to modify /etc/hosts.allow adding this line:
Now try it.
Login with different users on the same machine and:
$ mesg y $ talk user@localhost
“mesg y” allows write access in your terminal