Does anyone know of any reasonably good chat bot programs?

Any specific kind of chat bot or just a bot that can keep a normal conversation going?

Actually, I'm looking for one that can be tinkered with and used in your own project, but I'd settle for finding any bot that actually seems realistic when you talk to it. I went to one that was supposed to be good, and I was rolling my eyes immediately.

I'm thinking about writing my own deep learning algorithms and creating a chat bot from scratch (if I can't find a commercial chat bot that can be modified). Finding one that worked properly would help me learn what to do.