In addition to displaying the played notes, I've also added some interesting features such as note count, chord recognition, legato-ness score, and even calorie consumption, among others.

GitHub page (with a brief description): https://github.com/wiwikuan/pianometer

Use it online: https://nicechord.com/pianometer/

I also made an introductory video with English subtitles. If you're interested, you can check it out: https://www.youtube.com/watch?v=YsL7WGUEU-4