Though Ruby developers will say that Rails is vastly superior, Sinatra is another interesting framework to keep in mind when developing web apps with said language. Yes, even when it feels closer to a library than to a framework, Sinatra can still qualify as one, mainly because you can use its pre-written methods and abstractions to build simple Ruby-based applications. We could say, in fact, that Sinatra is a lightweight framework that feels like the perfect gateway to learning about Ruby web apps.

A web framework (WF) or web application framework (WAF) is a software framework that is designed to support the development of web applications including web services, web resources, and web APIs. Web frameworks provide a standard way to build and deploy web applications on the World Wide Web.