Are there any applications that can help me design a user interface in conceptual way?
closed as off topic by gnat, Yannis Rizos♦ Jun 13 '12 at 14:27
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If you are in a Microsoft space SketchFlow is relatively new and might be for you.
I Do believe that Balsamiq is the defacto standard, most used and most mature.
I haven't used either yet but the video's I have seen make me think SketchFlow is more for graphical designers than for developers.
If neither is good for you a nice list of GUI Prototyping tools can be found here
Are you looking for a mockup tool? If so then I can recommend Balsamiq
With this you can create a mockup of your page which looks like it has been drawn, so when you show it to other people (preferably your potential users) they don't have the expectation that it will do anything when they try.