Since an AI named Mycroft (after M. Holmes) is an essential part of the story "The Moon is a Harsh Mistress", I'm surprised it wasn't mentioned. Of course, it

Since an AI named Mycroft (after M. Holmes) is an essential part of the story "The Moon is a Harsh Mistress", I'm surprised it wasn't mentioned. Of course, it depended on trinary circuits and Loglan (a logic based programming language), neither of which exist in the form mentioned. There are some modern attempts to develop an AI. I would argue that Watson is not anything close to Mycroft, in purpose, nor in design.