The DotNET framework is an open standard and mono is the implementation for multiple platforms, including Linux, MacOSX and Windows. Mono is behind on the Microsoft dotNET framework, but there might be just enough features for your program to run on it.
You can develop with MonoDevelop which is my preferred development environment on MacOSX, a plugin is available to debug from Visual Studio and the Moma tool analyses your assemblied for mono compatibility.
A complete toolbox for every developer with C# knowledge, because there is no VB.net support.