can .Net application works on Macintosh?

What you need to do is to install Portable .NET on Mac OS X and then recompile your C# source code (just a text file, of course) so that the executable will run under that particular operating system.

Each implementation of .NET needs a runtime whose 'just in time' compiler can produce a native executable for the operating system and/or CPU which it's targetting.

To be realistic about this, if it's an application of any complexity, then it'll be a miracle if it will compile and run without any modifications at all on Mac OS !!

The parts of the .NET framework supported by Portable.NET will only be a subset of the full Microsoft .NET framework and some parts which are shared may not behave exactly the same. So I'd expect to have to do a fair bit of work to port and test your application.

 
 

I have just discovered, whilst answering a similar question, that there's a third .NET implementation which can target Mac OS X, namely Portable.NET.

Here are links to all three if you want to know more:

http://www.mono-project.com/Main_Page 

http://www.microsoft.com/downloads/details.aspx?FamilyId=3A1C93FA-7462-47D0-8E56-8DD34C6292F0&displaylang=en

http://dotgnu.info/

Incidentally, only v1.0 of the Microsoft SSCLI can target Mac OS X 10.2. The latest version 2.0 only targets Windows XP (+ SP2). 

If you're talking about .NET Compact Framework applications, then the answer is 'no'.

However, there are two free implementations of desktop .NET, namely Mono and the Microsoft SSCLI (formerly Rotor), which can target Mac OS X.