SiYuan is a personal knowledge management system centered around privacy protection, supporting block references and bidirectional linking. Written in TypeScript and Golang, it offers features such as block-level content organization, a WYSIWYG Markdown editor, content block snapshots, mind maps, back-linking, and references. SiYuan allows for nonlinear content organization, facilitates information connectivity, and aids in building a knowledge network. Moreover, SiYuan supports data self-hosting, ensuring user data security and privacy. It boasts an active community and a rich ecosystem of plugins, compatible with multiple operating systems including Windows, macOS, and Linux. Most features are free, with premium features available for a fee, such as data synchronization.