I guess it's really safe cause it's open source, you can make notes on your habits but don't really do that. Its simple. Really fast. Haven't found a way to connect it to notion. In general it's a great app to track you habits. Does its job. Not more, not less.
Habitica - Habitica is a free habit building and productivity application.
My Year Photo Book - All your year’s Facebook & Instagram moments, in a book!
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
The Twayback Machine - View your friends' old tweets for fun and trolling
HabitBull - HabitBull
Timehop - Your digital life history