A Talker is a Client-Server communication system that uses telnet as base protocol. The Talker is the Server and it accepts connections from the Client. The Server is the Talker by it's self. But the talker has no meaning if it has no Clients attached.
This way, the Talker definition extends from the Server's it self, to the Clients and to the people on the clients. A community is formed. A Talker is all this. The Server, the Clients, the coder and the users.
A Talker is made to talk. This is it's purpose. By the evolution in the internet communications, the people realized that the information was emotions-less. A talker evolved to fill this emptyness.
A Talker is a program. Although you can build a complete talker from scratch, there are some base programs (Talker bases) you can use to build a Talker. It much simpler and coder friendly (if that even exists...) to modify a Talker base into a real Talker. All you need to do is to add some commands an to give a new look. At least on most of the Talker bases.
The fact of a Talker is built on one or another base doesn't affect much the user. The interface may change, but the user rarely has a perception of the core of the Talker. Experienced users may see it but for the common user this doesn't mean much.
There are many bases for a Talker and that is the choice of the Talker coder. They choose this or another because they like the implementation or because they are in a given community that uses that base. That was what happened to me. This way, I can discuss bugs within this community and/or new implementations.