My idea is to have a box for the low note, the interval name, and the high note. Under each box will be checkboxes for all possible values of note or interval names. The user can use any exercise limits they can imagine, such as all intervals with a single note in the bass or only major thirds between all notes or just no accidentals in either note. For each question, two of the boxes will be filled, and the user must identify the third. For example, the low note box says A, the high note box says E, and the answer is a perfect fifth for the blank interval box. I'll even include keyboard shortcuts.
I'm visiting family this weekend, so plunkin' time is limited. I divided what little practice time I had yesterday between sight reading, ear training, SRV, and more arpeggios. I get to practice on a nice Martin 12-string for the next couple days while I'm not smelling it.