Free, no account. I want feedback from people who actually practice at a keyboard.
I started PianoGrid while helping my daughter with piano practice. I already had some music theory, and I wanted a page we could open at the keyboard for chords, inversions, scales, and labeled notes — without creating an account.
The first public version is up. If you sit at a piano, I would like to know whether the diagrams are clear enough to use while practicing, and which reference page should come next.