FSNotes vs Obsidian
Both FSNotes and Obsidian are Markdown plain-text editors that can be used to link together notes.
FSNotes
FSNotes is a powerful, keyboard-centric note-taking app with strong emphasis on security and speed. Unlike Obsidian, it is an Apple-exclusive app.
Obsidian
Obsidian is a lot more sophisticated in its note-linking abilities. You can easily build and navigate whole knowledge bases with Obsidian. That said, it's definitely more complicated than FSNotes.
Fan of Markdown note-taking apps? 🤔
Maybe Paper is what you're looking for.