I finally published a second item to the Tools page: the Triad Trainer. Like its predecessor, the Interval Trainer, it's just like computerized flash cards. You'll see three note names displayed, and the object is to identify the triad comprising the notes.
Features are limited for now. Only major and minor triads are displayed from a fixed range of notes. I'll soon enable fine tuning in the spirit of the Interval Trainer. Enjoy.