I need to develop a software which works for both windows and Mac OS.
The requirement are follows:
User can view flash file, make the selection and software print out the user selected flash file list.
I have experience in .net and windows platform but no experience in Mac OS. What is best development language and tool for my current situation.
I may be a bit biased on this, but you should use Qt because it will make your code portable on Windows, Mac OS X, Linux and even some mobile platforms. I don't really understand your requirement but Qt is pretty much the all-round cross-platform solution. It's C++ based, but easy as such (no memory management hassle, Qt takes care of it all).
On one hand you could use Java, it's fully compatible with Windows, Mac and Linux, also the language is similar to C# so you could adapt without too much trouble, if you used .net with C#.
On the other hand you could use your knowledge in .net and use Mono. It's an open source library for running .net code in other platforms, It's not equal to .net (doesn't include all the libraries) but could solve your problem.
Hope my answer helps you.