This plugin is only useful for Unity 4 free version users. Built-in sockets are already enabled in Unity 4 Pro and Unity 5 (both Personal and Pro).

This package allows you to integrate your Unity game with a Socket.IO back-end.

Bringing the fastest and most realiable real-time bidirectional engine to every platform, browser and device that supports Unity.

Good ol' Sockets allows to run a lot of popular assets that rely on .NET sockets, such as Tasharen Network, Photon Networking Free, UniWeb, BestHTTP and many others. If you ever wanted to use them, but have no Pro license for Android/iOS - this asset will save your day.