Doxygen - Generate documentation from source code
OpenAPI Generator - OpenAPI Generator enables you to generate documentation, clients, and servers from OpenAPI 2.0/3.x documents without hassle.
DocFX - A documentation generation tool for API reference and Markdown files!
Swagger Codegen - Swagger Codegen can reduce the complexities that arise in your build process by providing client SDKs and server stubs for any API you want.
Natural Docs - Natural Docs is an open-source documentation generator for multiple programming languages.
API Transformer - API Transformer is a powerful solution that enables you to Transform API specifications to any format.