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.
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HabitBull - HabitBull
Iteration X - Iteration X allows teams to annotate and edit any live website or web app directly in Chrome.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
EditMode - Update website texts in real-time and get a sharable link.