HumOn, but I haven't used it.

It is a music creation app for mobile devices. It lets you hum or whistle a melody and turns it into musical notation, with no need for music theory or instruments. You can edit the melody, choose from various musical genres, and export the result as a MIDI file for use in other software.

It uses artificial intelligence to turn your humming into sheet music. You simply record your hummed melody in the app; the AI analyzes the pitch and duration of each note and automatically generates the corresponding sheet music.