...

• Ruby: Sinatra, Rails
• Python: Flask, Django
• Java: JAX-RS (many implementations of standard API available), Quarkus, Spring, Restlet
• C#: ASP.NET Web API, ASP.NET Core MVC
• Go: Revel, Gin
• R: Plumber
• JavaScript: Express, Hapi

Development Tools

In addition to a Web API framework, the following tools may also prove useful:

• Apicurio and SwaggerHub: tools for designing and documenting APIs using the Open API description format 
• Postman and SoapUI: tools for API testing
• Microcks: tool for mocking and testing APIs, builds on Postman or SoapUI

Monitoring

The ability to monitor services provides many benefits to both the service owner and clients of the service:

...