It's pretty hard to do something that no one has done before. The same goes for communicating your thoughts and opinions to the world.
You are most likely not special, and that's okay.
Yes, there are countless note-taking apps already. But that shouldn't put you off. On one side, you still might learn from creating one. On the other, who says that your note-taking app won't be the one to rule them all?
And writing is no different. Just because other people already wrote about it doesn't mean everyone saw or heard of it.
Execution, ideas, writing styles, and audiences differ from person to person. Go ahead. Do whatever you want. Say whatever you want. And don't get discouraged just because you are not the first person to do so.