A free app for Android, by brAzzi Labs.
Riff Studio is a musical app that lets you create songs for practice and for performance. It is a music creation tool that lets you compose music and sing along with it in a musical way. The app has an audio engine that is based on the sound of instruments that you can play.
The app is designed for practice, so it allows you to adjust the tempo and the pitch to help you get your musical score right. It also provides a mechanism to adjust the pitch and the tempo at the same time, to get the perfect tempo for every note.
Besides from the in-app experience, you can export the songs you create as an MP3 file and save them to your device. You can also export them as WAV and MIDI files.