Json.NET

Json.NET is a popular high-performance JSON framework for .NET

Features

-Flexible JSON serializer to convert .NET objects to JSON and back again
-LINQ to JSON for manually reading and writing JSON
-High performance, faster than .NET's built-in JSON serializers
-Writes indented, easy to read JSON
-Convert JSON to and from XML
-Supports Silverlight and Windows Phone

The JSON serializer is a good choice when the JSON you are reading or writing maps closely to a .NET class. The serializer automatically reads and writes JSON for the class.