The main difference between the Web server and application server is that the webserver is meant to serve static pages

Web Server

It is a computer program that accepts the request for data and sends the specified documents. A web server may be a computer where the online content is kept. Essentially internet server is employed to host sites however there exist different web servers conjointly like recreation, storage, FTP, email, etc.

Application server

It encompasses Web container as well as EJB container. Application servers organize the run atmosphere for enterprise applications. The application server may be a reasonable server that means how to put the operating system, hosting the applications and services for users, IT services and organizations. In this, the user interface similarly as protocol and RPC/RMI protocols are used.

Thin

Thin is a very popular application server which claims itself to be the most “secure, stable, fast and extensible Ruby web server”. 

Unicorn

Unicorn is an HTTP server for Rack applications designed to only serve fast clients on low-latency, high-bandwidth connections and take advantage of features in Unix/Unix-like kernels. Slow clients should only be served by placing a reverse proxy capable of fully buffering both the request and response between the unicorn and slow clients.

Puma

Puma is a simple, fast, threaded, and highly concurrent HTTP 1.1 server for Ruby/Rack applications. Puma’s popularity as both a web and Rails server has shown steady growth toward the position of preferred tool for both roles. Growing out of the once-mighty Mongrel, Puma hails itself as “A Modern, Concurrent Web Server for Ruby”. 

Passenger

A modern web server and application server for Ruby, Python, and Node.js, optimized for performance, low memory usage and ease of use. It is a mature, feature-rich product that aims to cover the necessary needs and areas of application deployment whilst greatly simplifying the set-up and getting-started procedures. It is referred to as mod rails/mod rack for this very reason amongst the Ruby (Rails) community.

Difference between the web server and application server:

1. Web server encompasses web container only. While the application server encompasses Web container as well as EJB container.
2. Web server is useful or fitted for static content. Whereas the application server is fitted for dynamic content.
3. Web server consumes or utilizes less resources. While the application server utilizes more resources.
4. Web servers arrange the run environment for web applications. While application servers arrange the run environment for enterprise applications.
5. In web servers, multithreading is not supported. While in the application server, multithreading is supported.