Apps with 'Katex' feature
Mochi is a cross-platform desktop tool that lets you take notes and make flashcards using markdown, then study them using spaced repetition.Spaced Repetion
Wiki app with markdown editor
Start & Doc allow you to create and manage all your docs. Just as a content manager like Wikipedia, you can create pages, write on it your documents but also create links between them in the same way as a website.