Cowboy is the newest popular webserver on the Erlang scene. Created by Loic Hoguin, and under heavy development, it currently supports SPDY, WebSockets, and follows a model that differentiates itself from the other Erlang webservers: It doesn't maintain a process dictionary. Instead, it follows a more 'pure' flow, by passing around the a request object to each of Cowboy's functions. It's a lightweight, high performance webserver, and extermely capable.

Inets is the built-in Erlang Webserver. It's lightweight, and gets the job done. Its biggest benefit is that it does not require any external dependencies, since it's a part of the standard Erlang release. If you have a simple app that doesn't require much by way of high performance, Inets will work.

Mochiweb is a simple webserver that sticks mostly to maintenance releases these days, new features are rarely added. But it is a perfectly performant and lightweight server for most web application uses.

Webmachine is a webserver with an emphasis on REST. Its main focus is for making great RESTful APIs. The perfect use-case for using Webmachine with Nitrogen would be to provide a powerful RESTful API for external apps (like mobile device APIs), while also providing an interactive interface utilizing Nitrogen for web users.

Yaws is the granddaddy of Erlang webservers. It's tried and true, has been around for many years, and continues to improve, including adding Websocket support. It has solid performance metrics, and has a configuration system modelled after Apache's.

IN GENERAL if you are completely unsure which webserver to use, we recommend choosing either Cowboy or Yaws for production environments, as both provide quality performance, support websockets natively (though any server can support websockets in Nitrogen), and both handle large files smoothly.