Greendot was a punchcard for my weekly goals, and it's available on Android.

Select the number of days a week you want to do something, pick an emoji to represent the goal, and watch confetti explode every time you get a heart.

I used this app for a few months, and by then the habits that were going to stick had stuck, and I changed my mind or gave up on the rest and stopped using it.

An elegant entry into the crowded habit tracking space but more importantly a nice example of simple, small, personal software.