This piano app listens and corrects you—and gives you 5 years to master it

TL;DR: Learn piano with real-time feedback instead of passive videos. A 5-year flowkey Classic Plan is $99.99 (MSRP $899).
AppleInsider

How to play music using your Mac's keyboard with GarageBand's Musical Typing

Want to add elements to a GarageBand composition by playing a piano, but don't have access to a MIDI keyboard? Save money on buying a new instrument by taking advantage of the built-in Musical Typing ...
cursus.edu

Virtual keyboards: online music synthesizers on your keyboard

Virtual Piano - play, just play... Virtual piano Keyboard - extended keyboard, record mode. Virtual Online Piano with MIDI Functionality - Pressure-sensitive keys, chords, music theory, etc. Very rich ...