Microsoft Roslyn is the (former) name of the Microsoft .NET Compiler Platform, a set of open-source compilers and code analysis API for C# and Visual Basic.

Building upon these tools, DuoCode is able to understand all of the C# language features, including the new C# 6 syntax. Roslyn performs the code parsing, syntactic tree (AST) generation and contextual analysis, then DuoCode takes over to perform the code translation and generates JavaScript code (along with source-maps) while completing language features that exist in C# and are missing in JavaScript.

For more information, check out the Wikipedia article.