Some good music and singing apps are "Magic Piano" and "Sing! Karaoke," both by Smule. As of July 2015, both apps had four-star customer ratings on the Google Play Store.
In "Magic Piano" the player mimics the experience of playing a piano by using his fingers to tap the screen when a series of notes crosses the bottom of the display. A song may require the user to play one note at a time or multiple notes at once as a chord. Pressing notes with high accuracy leads to a high rating on the song, while the game penalizes players for missing too many notes or pressing them too early or too late.
In "Sing! Karaoke" players provide the vocals to songs by singing into the microphone. The game rewards players for singing the right melody even if the key is not the same, allowing players to sing songs outside of their natural vocal ranges. "Sing! Karaoke" has a multi-player game mode, in which players harmonize with a live duo partner.
Both apps let the user accumulate points by beating songs, taking third-party surveys or purchasing points with real-life money. Users spend points to unlock new songs and difficulties. Beating a song requires getting three stars on all difficulties. Most songs have three difficulty levels.