Dendron

Dendron is a developer-focused knowledge base that works as a VS Code extension. It uses a hierarchical note structure (like a file system) stored as plain Markdown, making it Git-friendly. It features powerful lookup, schemas for consistency, and publishing options. It's built for engineers, technical writers, and anyone comfortable in a code editor who wants a programmable, version-controlled knowledge base.

It's free and open-source. It ranks highly for technical users who value the power and extensibility of working within VS Code.