DirectPlay
DirectPlay is a deprecated API that was part of Microsoft's DirectX API. DirectPlay is a network communication library intended for computer game development, although its general nature certainly allows it to be used for other purposes.
DirectPlay is a high-level software interface between applications and communication services that makes it easy to connect games over the Internet, a modem link, or a network. DirectPlay features a set of tools that allow players to find game sessions and sites to manage the flow of information between hosts and players. It provides a way for applications to communicate with each other, regardless of the underlying online service or protocol. DirectPlay also resolves many connectivity issues, such as NAT.