Naming notes and playing a piece are two different skills. You can identify every note on a staff and still freeze when it is time to play, because playing demands the right pitch at the right instant, with no pause to think. That leap is exactly what this game trains: the score of a real piece scrolls across the screen and you play the melody.
Three modes and the tempo
There are three modes. Practice stops the score at every note and waits for you to play the right one: it is for learning the piece, and nothing is scored. In time lets the score run with a metronome and measures your playing — the right notes, and how precisely you attack each one. Play along scrolls in time and measures nothing: it is the mode for playing the harmony from the chord symbols. The tempo is yours: a 30 to 160 bpm control lets you learn the piece slowly before taking it up to speed.
How you answer
You can answer on the on-screen piano, on your computer keyboard, on a MIDI keyboard connected to your computer, or by playing into your microphone. With the microphone only pitch is measured, not rhythm: pitch detection lands after the attack, so timing it would mean inventing a precision that is not there.
The pieces
There are four public-domain pieces everyone knows by heart: Happy Birthday (the "Good Morning to All" melody, 1893), Twinkle, Twinkle, Little Star, Beethoven’s Ode to Joy and Jingle Bells. Melody only, no lyrics. Knowing the tune by ear helps more than you would think: when your reading goes wrong, you hear it straight away, no scoreboard needed. It runs right in your browser, on a computer, tablet or phone, with nothing to install.
Three of them already come with the chords written above the melody, so you can watch the feature work before writing your own. And the screen does not stop at the catalogue: you can load a MIDI file of your own and read your own music here, with the chords you plant yourself scrolling along with the melody. The file is read inside your browser; without an account it never leaves your device, and with one it is uploaded only when you tell it to sync.