Asio

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

Asio is a cross-platform C++ library for network programming that provides developers with a consistent asynchronous I/O model using a modern C++ approach.

Using Asio: How to use Asio in your applications. Includes information on library dependencies and supported platforms.
Tutorial: A tutorial that introduces the fundamental concepts required to use Asio, and shows how to use Asio to develop simple client and server programs.
Examples: Examples that illustrate the use of Asio in more complex applications.
Reference: Detailed class and function reference.
Design: Rationale and design information for Asio.