Installing Mono will allow you to run .Net applications in OS X – as long as they are 100% .Net and do not use any native Windows API’s. However, if you try to simply double-click on a .Net exe, OS X will not know what to do with it, or if you have VMware or wine installed, try to open that executable in another application.
To open a .Net exe with mono, you must open a terminal window, switch to the application directory, and type “mono Application.exe.” If you get an error stating something like “System.DllNotFoundException: gdiplus.dll” it’s probably because your application uses System.Windows.Forms, which must run under X11. To test X11, install the latest version and run the app again from the X11 terminal. Did it work? Great!
You probably don’t want to open X11 and type a command in terminal every time you want to run a .Net application, so you can make a script to do it for you. Open ScriptEditor (/Applications/Utilities/AppleScript/) and create a new script. Type something like:
do shell script "mono /Users/YOU/Downloads/YourApplication.exe"
Save the script as an Application and you’re done! Now you can run it just like any native OS X app. You can try it with SharpChess – just download the exe version. I was able to download the source of SharpChess, compile it with MonoDevelop on OS X and ran the exe I made on both Mono/OS X and Microsoft .Net/Windows. Unfortunately, Mono’s implementation of WinForms does not use the native Cocoa API, so it doesn’t look very good – I’ll work on that later.