Obsidian is a note-taking and organization app that uses a system of linked notes to help users organize and connect their ideas and information. It allows users to create and organize notes using a variety of formatting options, as well as to link notes together using cross-references and tags. Obsidian offers a range of features, including the ability to view and navigate notes in a variety of ways, as well as the ability to search and filter notes by content and metadata. It can be accessed on a variety of platforms, including Windows, Mac, iOS, iPadOS and Linux. Obsidian is known for its powerful note-linking and organization capabilities, making it a popular choice for users who need a flexible and feature-rich note-taking app.