With Solfège Scale you can learn to sing intervals.
On the tab pane Practice you can play notes as on a piano.
On the tab pane Sing you first hear the tonic, and then stars appear on a certain note which you have to sing before the answers sounds. The exercises go on until you go to another tab pane.
On the tab pane Listen you also first hear the tonic, and then another tone which you have to name.
Next to the do-re-mi scale you can select the 12 tone display. Also, the time between the question and the answer can be set, as well as the tonic and the maximal interval.
If you want to learn to sing better, then Solfège Scale is a valuable tool. Try to practice at least 10 minute per day. Aim for perfection. Only continue to a larger interval when you can sing (and name the notes) correctly for a few minutes.
And also take a look at my other solfège apps.
Enjoy!