Chatfuel is a platform that lets you build your own Chatbot for Messenger (and Telegram) for free. The only limit is if you pass more than 100,000 conversations per month, but for most businesses that won't be an issue. No understanding of code is required and it has a simple drag-and-drop interface. Think Wix/Squarespace for bots (side note: I have zero affiliation with Chatfuel).
The classic historic early chatbots are ELIZA (1966) and PARRY (1972).[10][11][12][13] More recent notable programs include A.L.I.C.E., Jabberwacky and D.U.D.E (Agence Nationale de la Recherche and CNRS 2006). While ELIZA and PARRY were used exclusively to simulate typed conversation, many chatbots now include functional features such as games and web searching abilities. In 1984, a book called The Policeman's Beard is Half Constructed was published, allegedly written by the chatbot Racter (though the program as released would not have been capable of doing so).[14]
There are obvious revenue opportunities around subscriptions, advertising and commerce. If bots are designed to save you time that you’d normally spend on mundane tasks or interactions, it’s possible they’ll seem valuable enough to justify a subscription fee. If bots start to replace some of the functions that you’d normally use a search engine like Google for, it’s easy to imagine some sort of advertising component. Or if bots help you shop, the bot-maker could arrange for a commission.

Chatbots – also known as “conversational agents” – are software applications that mimic written or spoken human speech for the purposes of simulating a conversation or interaction with a real person. There are two primary ways chatbots are offered to visitors: via web-based applications or standalone apps. Today, chatbots are used most commonly in the customer service space, assuming roles traditionally performed by living, breathing human beings such as Tier-1 support operatives and customer satisfaction reps.
Getting the remaining values (information that user would have provided to bot’s previous questions, bot’s previous action, results of the API call etc.,) is little bit tricky and here is where the dialogue manager component takes over. These feature values will need to be extracted from the training data that the user will define in the form of sample conversations between the user and the bot. These sample conversations should be prepared in such a fashion that they capture most of the possible conversational flows while pretending to be both an user and a bot.

Chatbots give businesses a way to deliver this information in a comfortable, conversational manner. Customers can have all their questions answered without the pressure or obligation that make some individuals wary of interacting with a live salesperson. Once they’ve obtained enough information to make a decision, a chatbot can introduce a human representative to take the sale the rest of the way.
As the above chart (source) illustrates, email click-rate has been steadily declining. Whilst open rates seem to be increasing - largely driven by mobile - the actual engagement from email is nosediving. Not only that, but it's becoming more and more difficult to even reach someone's email inbox; Google's move to separate out promotional emails into their 'promotions' tab and increasing problems of email deliverability have been top reasons behind this.
These are one of the major tools applied in machine learning. They are brain-inspired processing tools that actually replicate how humans learn. And now that we’ve successfully replicated the way we learn, these systems are capable of taking that processing power to a level where even greater volumes of more complex data can be understood by the machine.
An ecommerce website’s user interface is an important part of the overall application. It has amazing product pictures for shoppers to look at. It has an advanced search tool to help the shopper locate products. It has lovely buttons users can click to add products to the shopping cart. And it has forms for entering payment information or an address.
This is the big one. We worked with one particular large publisher (can’t name names unfortunately, but hundreds of thousands of users) in two phases. We initially released a test phase that was sort of a “catch all”. Anyone could message a broad keyword to their bot and start a campaign. Although we had a huge number of users come in, engagement was relatively average (87% open rate and 27.05% click-through rate average over the course of the test). Drop off here was fairly high, about 3.14% of users had unsubscribed by the end of the test.

ELIZA's key method of operation (copied by chatbot designers ever since) involves the recognition of clue words or phrases in the input, and the output of corresponding pre-prepared or pre-programmed responses that can move the conversation forward in an apparently meaningful way (e.g. by responding to any input that contains the word 'MOTHER' with 'TELL ME MORE ABOUT YOUR FAMILY').[9] Thus an illusion of understanding is generated, even though the processing involved has been merely superficial. ELIZA showed that such an illusion is surprisingly easy to generate, because human judges are so ready to give the benefit of the doubt when conversational responses are capable of being interpreted as "intelligent".