Obsidian

Obsidian is a new type of note-taking software that pushes the boundaries of what a note-taking app can and should do. It, like Notion and Roam Research (which didn't make the list due to their lack of offline support), aspires to be an all-encompassing digital database for your life—and sort of succeeds. Obsidian has a considerably higher learning curve than the other applications on our list, so only consider it if you're willing to put in the effort to configure it to your specific needs. At its foundation, it's just a notes software that uses Markdown-formatted text files, but things can become complicated quickly.

You may use the sidebar to organize your notes into folders and subfolders, but more importantly, you can link between them using internal hyperlinks. Typing "[[" brings up a dialog window where you may choose any other note to connect to. This means you can simply refer to previously written notes; for example, you may make a list of all the books you've read in the last year and link to the notes where you review them.

Furthermore, you can virtually personalize everything you desire. You have complete control over the interface and may have as many notes open in the same window as you desire. There are also community plugins that add functionality such as a kanban board, taking it well beyond plain text files.

Detailed information:

Cost: Free + Pro for $1.49/Month
Platforms: Android, iOS

Download: https://obsidian.md/download