If we are talking about the same piece of software, the MindReader that I know lets a user to describe him/herself by choosing a bunch of words. It then synthesizes a report describing your personality traits. In that sense, it does not really read your mind, instead of putting together the words you chosen to describe you. Juji on the other hand automatically derives your traits based on your word use in your own informal communication content. For example, in MindReader, you have to tell it you are "ambitious" by choosing the word, while Juji infers whether you are ambitious or not by various word use patterns even if you have never mentioned the word "ambitious" or its synonyms.