I've created an open source TCP Client/Server project that is on GitHub as well.  The server runs on Windows and is implemented in C#.  The server also includes a Windows Authentication protocol, however; any authentication method can easily be implemented.  The project includes client APIs for Windows (C#), Android (Java), iOS/OSX (Objective-C).  I have also created an object access protocol that supports serialization of server-side C# objects, supports remote method invocation, passing of objects and arrays, variable (Property) subscriptions as well as event notifications.  Although I haven't open sourced the object access protocol, I would like to offer the protocol to any developers that are interested in trying out the API.  I will offer a free redistribution license.  Please contact me at my email address or goto my website.