Habits
Tap a day to mark it done, tap again to undo. A dashed square is a free day for a habit you do a few times a week.
Archived
Use it as an app
It works offline once it's opened here. In Chrome, open the ⋮ menu and choose Add to home screen (or Install app) to get an icon that opens it full screen.
Move to another device
Your habits are saved in this browser only. Export them to a file, then import that file on your phone or laptop.