Prima Vista is a free sight-singing studio by Jason Zac at Nathaniel School of Music in Bangalore. You read from the stave, you sing, and the app listens to what you actually sang. It is for singers who want to practise from notation in a browser, with a microphone, not on a silent worksheet.
Every note is marked twice: once for pitch and once for time, so you can see which of the two let you down. The library behind that marking is 995 graded exercises, including 576 method exercises across 23 units and 103 public-domain hymns. Transpose any line to G if that is where your voice sits — the first Melodia exercise is written in C.
Hear it plays the line on the piano. Sing it gives one bar of clicks, then marks you. Space starts and stops a take. Use headphones with accompaniment so the microphone hears you and not the piano. This is a practice studio, not a singing course.
The strip above the studio is the school path. When you want this material taught as voice training, build your voice with singing classes. For other free lessons from the same school, explore free music lessons.