My favorite variant: https://novayashkola.org/janko/ , https://en.wikipedia.org/wiki/Jank%C3%B3_keyboard , https://en.wikipedia.org/wiki/Isomorphic_keyboard

Since a year ago, I found that I can play songs by ear on the Janko keyboard far more easily than on standard piano keyboards.

More resources: https://github.com/wcgbg/terpstrakeyboard/ , https://www.youtube.com/results?search_query=janko%20keyboar...