We have searched online and found some decent resources, either free or at least you can try for free. Of course, there are many other websites and we will amend to this thread as we discovery them.
(1) flowkey
App: flowkey
Website: https://www.flowkey.com/en
Review:
Lessons range from beginner to advanced
Have practice songs as lesson progress
Basic music theory
(2) Piano Lessons
Website: https://www.pianolessons.com/
Review: combines online tutorials with videos. Also good resources for basic music theory. However, I do not think it covers enough basic and might be daunting for beginners.
(3) PIANO-OLOGY
Website: https://piano-ology.com/
Review:
Although this site does not have any recent update, it does have cover some basic topics for beginners.
(4) Pianonanny
Website: https://pianonanny.com/
Review: Feels like a bit old school (but better than zebrakeys) and could a bit boring to read through the materials. Quality and systematic material. Downside: I feel like no video is a big thumb-down as you cannot see the finger movement.
(5）Skoove APP
This website partner with Roland and Roland customers can have a few months of free classes.
(6) Simply Piano
Website: https://www.pianodreamers.com/simply-piano-review/
Review: great reviews from many, and free initially, but will cost some if you need full access.
(7) Udemy
Website: https://www.udemy.com/topic/piano/free/
Review: Hey! No need to read my review here, there are thousands of review on site!