ChatScript is the next generation chatbot engine that won the 2010 Loebner Prize with Suzette, 2011 Loebner with Rosette, and 2nd in 2012 Loebner with Angela (a bug I introduced in the Loebner protocol, not the engine). The technology behind Outfit7's mobile app Tom Loves Angela and ESL chatbots at Japan's SpeakGlobal. 3rd place winner Chatbot Battles 2012 and awarded best 15 minute conversation prize.
Also has useful ontology files for nouns, verbs, adjectives, adverbs. Stand-alone or server modes. LINUX and Windows (Visual Studio 8 and 10) and Mac/iOS.