Pedagogical research demonstrates theories and practices of perception or production of melodic or harmonic ``intonation'', i.e. the realization of pitch accuracy. There are software and hardware to help students improve intonation. Those tools have various functions. Nevertheless, they still miss something which could benefit users very much. Even worse, they are not easy to be revised. Most importantly, there should be more amusing and engaging interaction between a tuning trainer and a user which is able to exchange roles of tuner and player. In this research, we implement an open-source program named ``Harmonic Intonation Trainer'' in Pure Data. It includes most of essential elements of a smart tuner. A user can tune his pitch while optionally hearing (through earphones) the target pitch and other harmonic intervals in respective octaves. Moreover, in its interactive accompanist mode, a user's input pitch serves as the reference frequency; the program follows his intonation to generate corresponding harmonic intervals. Additionally, user can straightforwardly edit all parameters and patches by Pure Data. Any adoption or revision is absolutely welcome. Finally, we will initiate another research to test and to inspect experimental results from student orchestras so that its future version is expected to be more sophisticated.