What is the most intelligent chatterbot available for free online?

A chatterbot (or chatbot, as it is sometimes reffered to) is a program designed to simulate intelligent conversation with a human through text or speech. I want to know which one is the most intelligent (and I don't want ones that search for keywords and respond appropriately from a database. I want one that actually uses complicated algorithms to create conversation.) It must also not contain innappropriate content. I want the one that can give the most lifelike conversations. (And please, don't give me one of those stupid answers where you say I should just talk to someone in real life.)