The Microsoft Bot Framework is now in preview and it seems very interesting: it is what you need to build and connect intelligent bots that interact naturally wherever your users are talking, from text/sms to Skype, Slack, Office 365 mail, Facebook Messenger and other popular services. It enables organizations to build intelligent agents, known as Bots, that can interact with a requesting user. The primary interface for these experiences is email, text or voice. Conversation-driven UI can help to handle a conversation for grabbing a taxi, paying the electric bill, sending money to a friend, choose the sandwich you want or whatever.
If you want to know more about it you can follows the following links:
Programmatically you can also send a message to a user, knowing his conversation id and to send “not explicitly requested” messages you must go through the Bot Connector: http://docs.botframework.com/connector/replying; http://docs.botframework.com/connector/new-conversations/#navtitle