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!
Widdershins - Widdershins is an open-source, easy to use Semoasa/ OpenAPI/ AsyncAPI/ definition to ReSlate/Slate compatible markdown released under the MIT License.
NDoc - NDoc generates class library documentation from .
API Spec Converter - API Spec Converter is an open-source solution that enables you to transform API descriptions between major formats like WADL, OpenAPI (fka Swagger), API Blueprint, RAML, and more.