What is Shareware?  
Shareware is a marketing method, not a type of software or even strictly just a distribution method. When software is marketed through normal retail channels, you are forced to pay for the product before you've even seen it. The Shareware marketing method lets you try a program before you buy it. Since you've tried the program, you know whether it will meet your needs before you pay for it. A Shareware program is just like a program you find in major stores, catalogs, and other places where software is purchased; except you get to use it, on your own computer, before paying for it.  
 
Why Pay For Software I Already Have?
 
Basically, for the same reason you should pay for any program: because it is the honest thing to do. Shareware is commercial software, fully protected by copyright laws. Like other business owners, shareware authors expect to earn money for making their software available. In addition, by paying you may then be entitled to additional functions, removal of time limiting or limits on use, removal of so-called "nag" screens, and other things as defined in the documentation provided by the program's author.  
 
from: The Association of Shareware Professionals  
http://www.asp-shareware.org/1-faq.asp#share
 
 
 
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