I found that I am confusing between web framework and web server.
Apache is a web server.
Tornado is a web server written in Python.
Nginx is a web server written in C
Zend is a web framework in php
Flask/Bottle is a web framework in Python
RoR is a web framework written in Ruby
Express is a web framework in write in JS under Node.JS
Web server can refer to either the hardware (the computer) or the software (the computer application) that helps to deliver content that can be accessed through the Internet.1
The primary function of a web server is to deliver web pages on the request to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and scripts.
A web server is the basic to delivering requests/pagess to the clients/user on the internet
A web application framework is a software framework that is designed to support the development of dynamic websites, web applications and web services. The framework aims to alleviate the overhead associated with common activities performed in Web development. For example, many frameworks provide libraries for database access, templating frameworks and session management, and they often promote code reuse.
A web framework uses a webserver to deliver the requests to client, but it is not the web server.
You can also write web server with node.js as you can see on the front page of node.js. In the beginning Ryan said you could put Nginx in front of node.js because of the stabilty of the project. The project was and still is pretty young. Nginx is a proven web server that will keep on running while node.js can crash. Then again a lot of user just use node.js for that.