Smule is a mobile karaoke app available for Android (and iOS). It[SQ]s not *the only* singing app, but it[SQ]s a very popular one, known for its features allowing users to sing along to various songs, record themselves, and share their performances with others. The "The 1 Singing App" is a marketing claim, and while it might have a large user base, many other competing karaoke apps exist.