OpenAPI.NET

OpenAPI.NET on GitHub
"The OpenAPI.NET SDK contains a useful object model for OpenAPI documents in .NET along with common serializers to extract raw OpenAPI JSON and YAML documents from the model."

OpenAPI in Microsoft Docs
"REST APIs are often described using an OpenAPI definition (formerly known as a Swagger file). This definition contains information about what operations are available in an API and how the request and response data for the API should be structured."

Open API

import.io

Azure API Management

Swagger

OData

APIs.json

AsyncAPI

links from:

.NET Rocks! vNext