I loved reading Atomic Habits during the first lockdown. I was excited to try out its actionables, specially tracking to keep me honest.
I tried a bunch of iOS apps, but wanted no friction, no tracking, no cloud, no social, etc. so eventually built https://flathabits.com. Also wanted to own my habit data (as plain text), so I made sure Flat Habits stored its data locally as an org file.
I'm an Emacs nutter and can say the strength of a habit tracker lies in removing daily friction from the tracking process itself. The plain text part is cherry on top (bringing piece of mind around lock-in). In my case, it's been months since I looked at the plain text file itself.
As for forming habits themselves (the actual goal)... it's been well over a year since I started running. I've kept it up since reading Atomic Habits (and started tracking).
I too would love an android app.
Ad-free and FOSS: https://github.com/iSoron/uhabits