From the Facebook code blog:
One of the long-term goals in AI is to develop intelligent chat bots that can converse with people in a natural way. Existing chat bots can sometimes complete specific independent tasks but have trouble understanding more than a single sentence or chaining subtasks together to complete a bigger task. More complex dialog, such as booking a restaurant or chatting about sports or news, requires the ability to understand multiple sentences and then reason about those sentences to supply the next part of the conversation. Since human dialog is so varied, chat bots must be skilled at many related tasks that all require different expertise but use the same input and output format. To achieve these goals, it is necessary to build software that unifies these tasks, as well as the agents that can learn from them.