All chatterbots are not the same... Here is a brief typology of the different bots available

A wide variety of chatterbots can be found in the AgentLand directory:
http://www.agentland.com/6Artificial_Life/Chatterbots

On or off-line

Chatterbots can be part of a web site, and you chat to them on-line, like Cybelle. This is probably the most common form of access at the current time. Some people even put their bots on Instant Messenger or IRC - so the next time you get into a strange conversation, ask yourself whether you are talking to a man or a machine! ;-)

Others can be downloaded to your computer. There you are able to really get to know your chatterbot in detail, find out its strong points and weak areas, and modify its knowledge base. A number of them can be accessed both on- and off-line.

Type of interface

How do you communicate with a chatterbot? Frequently, by typing text into a box. This method is effective but not very convivial, so many chatterbots have an animated figure to encourage interaction, using a photo-realistic image, a cartoon or some other graphic. Some chatterbots have a Text-To-Speech interface, so that you can talk to them through a microphone and hear their replies. This conversational interface can add to the illusion of reality.

Role

Is your chatterbot designed for general conversation? To be a friend and assistant? Does it have a particular personality of its own? Famous people reincarnated on the Web as a chatterbot include Elvis and John Lennon. Does it have a commercial function? Does it guide you around a site, provide help in finding the product you want, deal with your questions, offer to put you in contact with humans in the sales team? Chatterbots can be some or all of these things, and many others besides.

Chatterbots available on the Internet today generally have one of two main roles:

Conversational chatterbots aim is just that, to chat. They are often the result of the work of academic research, or passionate individuals or groups seeking to push back the barriers in communication between man and machines. This in no way excludes conversational chatterbots from having commercial applications, or being able to provide certain services such as launching programs on your computer.

Commercial chatterbots are designed to fulfill a specific function, for example to be part of a Web-based customer relation management strategy. A tireless employee, working 24/7, they offer a pleasant and useful first contact to customers, and are able to deal with the most common problems or requests for information. The objective for these chatterbots is to be good at their particular job, rather than to be an expert in general conversation, though once again, nothing prevents them from being able to talk about a wide range of topics, if their botmaster wishes.

Cost

Prices for chatterbots range from absolutely free to costing hundreds of thousands of dollars for a fully implemented commercial chatterbot. But you can talk to all the chatterbots you find on the web for free - that's what they're there for!