MidiSlayer listens to a MIDI keyboard and drills sight-reading against 69 pieces, from Twinkle Twinkle to the complete Goldberg Variations. Its note-weighting is literal: a never-seen note is ×10 more likely to reappear, a missed one ×4, a known one ×0.5. Free gets the whole reading course, one arcade run a day and a jam with “The Session” — real drums and a double bass that count you in and listen to how hard you play; $49.99, once, unlocks all nine modes, the full library and your own MusicXML.