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.
Future Me - Send an email to your future self
Habitica - Habitica is a free habit building and productivity application.
Letter to my future self - Letter to my future self is a prominent email scheduling service that gives you the opportunity to create a letter with goals and thoughts for your future self and schedule a date for sending it.
HabitBull - HabitBull
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.