JSON : JSON (JavaScript Object Notation) is a lightweight data-interchange text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.

JSON.NET : This is a popular high-performance JSON framework for .NET

JSON.NET Features:
Flexible JSON serializer for converting between .NET objects and JSON
LINQ to JSON for manually reading and writing JSON
High performance, faster than .NET’s built-in JSON serializers
Write indented, easy to read JSON
Convert JSON to and from XML
Supports .NET 2, .NET 3.5, .NET 4, Silverlight, Windows Phone and Windows 8.