Grasshopper
From the product description: Grasshopper is a Visual Studio .NET plug-in, which enables you to use C# or Visual Basic .NET to develop, debug and deploy Web applications and Web services that run on Microsoft Windows, Linux and any Java-enabled platform. Grasshopper introduces a patent-pending compiler that compiles Microsoft Intermediate Language (MSIL) into standard Java bytecode. You can access external Java components regardless of the Java development environment in which they were originally developed.