Even though EarTrain targets primarily those who want to develop perfect pitch, you can still use it to practice your relative pitch! With great success I might add! The only limit (as always) is your imagination.
This is how I tweaked it to practice relative pitch.
Be careful though, this will work only if you have some basic music theory knowledge. (Scales, etc) Not recommended for total beginners. Let’s say that you’d like to practice the c-major scale (like you would do in a conservatory). All you have to do is go to custom test and choose the c major scale notes. That’s it! Start the test, EarTrain plays the notes for you, one at a time, and you get a good practice of the c major scale!
You can do the same with e.g., G# minor scale, pentatonic scale, frygian mode, etc. Once again, the only limit is your imagination! 😉
In the end, everything breaks down to individual notes.