Ask HN: Current Chatbots/Natural Language Processing etc

Hi. I have recently got interested in chatterbots (like cleverbot etc). I found a Ask Hn about them from about two years ago (http://news.ycombinator.com/item?id=943590) but wanted to see if anyone has done any more (exciting) work on things like chatterbots/natural language problems. I have run into a few cool sites like cleverbot and jabberwacky but their code is not open source. I was hoping to find ways I could learn to make ones like that! So any thoughts on the idea of chatbots or projects or tutorials related to chatbots or natural language would be greatly appreciated. Thanks!