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.
Stoic Life Calendar - A digital Stoic Calendar built in Notion around the principle of Memento Mori; remembering that you'll die.
HabitBull - HabitBull
Stoic Life OS - Manage your entire life as a Stoic in one place, digitally.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Storycell - Interactive life calendar